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# Expression API

DataFrame methods such as `select` and `filter` accept one or more logical expressions and there are many functions
available for creating logical expressions. These are documented below.

:::{tip}
Most functions and methods may receive and return an `Expr`, which can be chained together using a fluent-style API:

```rust
use datafusion::prelude::*;
// create the expression `(a > 6) AND (b < 7)`
col("a").gt(lit(6)).and(col("b").lt(lit(7)));

```

:::

## Identifiers

| Syntax     | Description                                  |
| ---------- | -------------------------------------------- |
| col(ident) | Reference a column in a dataframe `col("a")` |

:::{note}
ident
: A type which implement `Into<Column>` trait
:::

## Literal Values

| Syntax     | Description                                        |
| ---------- | -------------------------------------------------- |
| lit(value) | Literal value such as `lit(123)` or `lit("hello")` |

:::{note}
value
: A type which implement `Literal`
:::

## Boolean Expressions

| Syntax              | Description |
| ------------------- | ----------- |
| and(x, y), x.and(y) | Logical AND |
| or(x, y), x.or(y)   | Logical OR  |
| !x, not(x), x.not() | Logical NOT |

:::{note}
`!` is a bitwise or logical complement operator in Rust, but it only works as a logical NOT in expression API.
:::

:::{note}
Since `&&` and `||` are logical operators in Rust and cannot be overloaded these are not available in the expression API.
:::

## Bitwise Expressions

| Syntax                                      | Description |
| ------------------------------------------- | ----------- |
| x & y, bitwise_and(x, y), x.bitand(y)       | AND         |
| x \| y, bitwise_or(x, y), x.bitor(y)        | OR          |
| x ^ y, bitwise_xor(x, y), x.bitxor(y)       | XOR         |
| x << y, bitwise_shift_left(x, y), x.shl(y)  | Left shift  |
| x >> y, bitwise_shift_right(x, y), x.shr(y) | Right shift |

## Comparison Expressions

| Syntax      | Description           |
| ----------- | --------------------- |
| x.eq(y)     | Equal                 |
| x.not_eq(y) | Not Equal             |
| x.gt(y)     | Greater Than          |
| x.gt_eq(y)  | Greater Than or Equal |
| x.lt(y)     | Less Than             |
| x.lt_eq(y)  | Less Than or Equal    |

:::{note}
Comparison operators (`<`, `<=`, `==`, `>=`, `>`) could be overloaded by the `PartialOrd` and `PartialEq` trait in Rust,
but these operators always return a `bool` which makes them not work with the expression API.
:::

## Arithmetic Expressions

| Syntax           | Description    |
| ---------------- | -------------- |
| x + y, x.add(y)  | Addition       |
| x - y, x.sub(y)  | Subtraction    |
| x \* y, x.mul(y) | Multiplication |
| x / y, x.div(y)  | Division       |
| x % y, x.rem(y)  | Remainder      |
| -x, x.neg()      | Negation       |

## Math Functions

| Syntax                | Description                                       |
| --------------------- | ------------------------------------------------- |
| abs(x)                | absolute value                                    |
| acos(x)               | inverse cosine                                    |
| acosh(x)              | inverse hyperbolic cosine                         |
| asin(x)               | inverse sine                                      |
| asinh(x)              | inverse hyperbolic sine                           |
| atan(x)               | inverse tangent                                   |
| atanh(x)              | inverse hyperbolic tangent                        |
| atan2(y, x)           | inverse tangent of y / x                          |
| cbrt(x)               | cube root                                         |
| ceil(x)               | nearest integer greater than or equal to argument |
| cos(x)                | cosine                                            |
| cosh(x)               | hyperbolic cosine                                 |
| degrees(x)            | converts radians to degrees                       |
| exp(x)                | exponential                                       |
| factorial(x)          | factorial                                         |
| floor(x)              | nearest integer less than or equal to argument    |
| gcd(x, y)             | greatest common divisor                           |
| isnan(x)              | predicate determining whether NaN/-NaN or not     |
| iszero(x)             | predicate determining whether 0.0/-0.0 or not     |
| lcm(x, y)             | least common multiple                             |
| ln(x)                 | natural logarithm                                 |
| log(base, x)          | logarithm of x for a particular base              |
| log10(x)              | base 10 logarithm                                 |
| log2(x)               | base 2 logarithm                                  |
| nanvl(x, y)           | returns x if x is not NaN otherwise returns y     |
| pi()                  | approximate value of π                            |
| power(base, exponent) | base raised to the power of exponent              |
| radians(x)            | converts degrees to radians                       |
| round(x)              | round to nearest integer                          |
| signum(x)             | sign of the argument (-1, 0, +1)                  |
| sin(x)                | sine                                              |
| sinh(x)               | hyperbolic sine                                   |
| sqrt(x)               | square root                                       |
| tan(x)                | tangent                                           |
| tanh(x)               | hyperbolic tangent                                |
| trunc(x)              | truncate toward zero                              |

:::{note}
Unlike to some databases the math functions in Datafusion works the same way as Rust math functions, avoiding failing on corner cases e.g.

```sql
select log(-1), log(0), sqrt(-1);
+----------------+---------------+-----------------+
| log(Int64(-1)) | log(Int64(0)) | sqrt(Int64(-1)) |
+----------------+---------------+-----------------+
| NaN            | -inf          | NaN             |
+----------------+---------------+-----------------+
```

:::

## Conditional Expressions

| Syntax                                                                                                                                                                                     | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |   |
| coalesce([value, ...])                                                                                                                                                                     | Returns the first of its arguments that is not null. Null is returned only if all arguments are null. It is often used to substitute a default value for null values when data is retrieved for display.                                                                                                                                                                                                                                                                                                                                                                                                                    |
| case(expr)</br>&nbsp;&nbsp;&nbsp;&nbsp;.when(expr)</br>&nbsp;&nbsp;&nbsp;&nbsp;.end(),</br>case(expr)</br>&nbsp;&nbsp;&nbsp;&nbsp;.when(expr)</br>&nbsp;&nbsp;&nbsp;&nbsp;.otherwise(expr) | CASE expression. The expression may chain multiple `when` expressions and end with an `end` or `otherwise` expression. Example:</br> <pre><code>case(col("a") % lit(3))</br>&nbsp;&nbsp;&nbsp;&nbsp;.when(lit(0), lit("A"))</br>&nbsp;&nbsp;&nbsp;&nbsp;.when(lit(1), lit("B"))</br>&nbsp;&nbsp;&nbsp;&nbsp;.when(lit(2), lit("C"))</br>&nbsp;&nbsp;&nbsp;&nbsp;.end()</code></pre>or, end with `otherwise` to match any other conditions: <pre><code>case(col("b").gt(lit(100)))</br>&nbsp;&nbsp;&nbsp;&nbsp;.when(lit(true), lit("value > 100"))</br>&nbsp;&nbsp;&nbsp;&nbsp;.otherwise(lit("value <= 100"))</code></pre> |
| nullif(value1, value2)                                                                                                                                                                     | Returns a null value if `value1` equals `value2`; otherwise it returns `value1`. This can be used to perform the inverse operation of the `coalesce` expression.                                                                                                                                                                                                                                                                                                                                                                                                                                                            |

## String Expressions

| Syntax                                         | Description                                                                                                                                                                                                                              |
| ---------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| ascii(character)                               | Returns a numeric representation of the character (`character`). Example: `ascii('a') -> 97`                                                                                                                                             |
| bit_length(text)                               | Returns the length of the string (`text`) in bits. Example: `bit_length('spider') -> 48`                                                                                                                                                 |
| btrim(text, characters)                        | Removes all specified characters (`characters`) from both the beginning and the end of the string (`text`). Example: `btrim('aabchelloccb', 'abc') -> hello`                                                                             |
| char_length(text)                              | Returns number of characters in the string (`text`). The same as `character_length` and `length`. Example: `char_length('lion') -> 4`                                                                                                    |
| character_length(text)                         | Returns number of characters in the string (`text`). The same as `char_length` and `length`. Example: `character_length('lion') -> 4`                                                                                                    |
| concat(value1, [value2 [, ...]])               | Concatenates the text representations (`value1, [value2 [, ...]]`) of all the arguments. NULL arguments are ignored. Example: `concat('aaa', 'bbc', NULL, 321) -> aaabbc321`                                                             |
| concat_ws(separator, value1, [value2 [, ...]]) | Concatenates the text representations (`value1, [value2 [, ...]]`) of all the arguments with the separator (`separator`). NULL arguments are ignored. `concat_ws('/', 'path', 'to', NULL, 'my', 'folder', 123) -> path/to/my/folder/123` |
| chr(integer)                                   | Returns a character by its numeric representation (`integer`). Example: `chr(90) -> 8`                                                                                                                                                   |
| initcap                                        | Converts the first letter of each word to upper case and the rest to lower case. Example: `initcap('hi TOM') -> Hi Tom`                                                                                                                  |
| left(text, number)                             | Returns a certain number (`number`) of first characters (`text`). Example: `left('like', 2) -> li`                                                                                                                                       |
| length(text)                                   | Returns number of characters in the string (`text`). The same as `character_length` and `char_length`. Example: `length('lion') -> 4`                                                                                                    |
| lower(text)                                    | Converts all characters in the string (`text`) into lower case. Example: `lower('HELLO') -> hello`                                                                                                                                       |
| lpad(text, length, [, fill])                   | Extends the string to length (`length`) by prepending the characters (`fill`) (a space by default). Example: `lpad('bb', 5, 'a') → aaabb`                                                                                                |
| ltrim(text, text)                              | Removes all specified characters (`characters`) from the beginning of the string (`text`). Example: `ltrim('aabchelloccb', 'abc') -> helloccb`                                                                                           |
| md5(text)                                      | Computes the MD5 hash of the argument (`text`).                                                                                                                                                                                          |
| octet_length(text)                             | Returns number of bytes in the string (`text`).                                                                                                                                                                                          |
| repeat(text, number)                           | Repeats the string the specified number of times. Example: `repeat('1', 4) -> 1111`                                                                                                                                                      |
| replace(string, from, to)                      | Replaces a specified string (`from`) with another specified string (`to`) in the string (`string`). Example: `replace('Hello', 'replace', 'el') -> Hola`                                                                                 |
| reverse(text)                                  | Reverses the order of the characters in the string (`text`). Example: `reverse('hello') -> olleh`                                                                                                                                        |
| right(text, number)                            | Returns a certain number (`number`) of last characters (`text`). Example: `right('like', 2) -> ke`                                                                                                                                       |
| rpad(text, length, [, fill])                   | Extends the string to length (`length`) by prepending the characters (`fill`) (a space by default). Example: `rpad('bb', 5, 'a') → bbaaa`                                                                                                |
| rtrim                                          | Removes all specified characters (`characters`) from the end of the string (`text`). Example: `rtrim('aabchelloccb', 'abc') -> aabchello`                                                                                                |
| digest(input, algorithm)                       | Computes the binary hash of `input`, using the `algorithm`.                                                                                                                                                                              |
| split_part(string, delimiter, index)           | Splits the string (`string`) based on a delimiter (`delimiter`) and picks out the desired field based on the index (`index`).                                                                                                            |
| starts_with(string, prefix)                    | Returns `true` if the string (`string`) starts with the specified prefix (`prefix`). If not, it returns `false`. Example: `starts_with('Hi Tom', 'Hi') -> true`                                                                          |
| strpos                                         | Finds the position from where the `substring` matches the `string`                                                                                                                                                                       |
| substr(string, position, [, length])           | Returns substring from the position (`position`) with length (`length`) characters in the string (`string`).                                                                                                                             |
| translate(string, from, to)                    | Replaces the characters in `from` with the counterpart in `to`. Example: `translate('abcde', 'acd', '15') -> 1b5e`                                                                                                                       |
| trim(string)                                   | Removes all characters, space by default from the string (`string`)                                                                                                                                                                      |
| upper                                          | Converts all characters in the string into upper case. Example: `upper('hello') -> HELLO`                                                                                                                                                |

## Array Expressions

| Syntax                                         | Description                                                                                                                                                                                                                                                                      |
| ---------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| array_any_value(array)                         | Returns the first non-null element in the array. `array_any_value([NULL, 1, 2, 3]) -> 1`                                                                                                                                                                                         |
| array_append(array, element)                   | Appends an element to the end of an array. `array_append([1, 2, 3], 4) -> [1, 2, 3, 4]`                                                                                                                                                                                          |
| array_concat(array[, ..., array_n])            | Concatenates arrays. `array_concat([1, 2, 3], [4, 5, 6]) -> [1, 2, 3, 4, 5, 6]`                                                                                                                                                                                                  |
| array_has(array, element)                      | Returns true if the array contains the element `array_has([1,2,3], 1) -> true`                                                                                                                                                                                                   |
| array_has_all(array, sub-array)                | Returns true if all elements of sub-array exist in array `array_has_all([1,2,3], [1,3]) -> true`                                                                                                                                                                                 |
| array_has_any(array, sub-array)                | Returns true if any elements exist in both arrays `array_has_any([1,2,3], [1,4]) -> true`                                                                                                                                                                                        |
| array_dims(array)                              | Returns an array of the array's dimensions. `array_dims([[1, 2, 3], [4, 5, 6]]) -> [2, 3]`                                                                                                                                                                                       |
| array_distinct(array)                          | Returns distinct values from the array after removing duplicates. `array_distinct([1, 3, 2, 3, 1, 2, 4]) -> [1, 2, 3, 4]`                                                                                                                                                        |
| array_element(array, index)                    | Extracts the element with the index n from the array `array_element([1, 2, 3, 4], 3) -> 3`                                                                                                                                                                                       |
| empty(array)                                   | Returns true for an empty array or false for a non-empty array. `empty([1]) -> false`                                                                                                                                                                                            |
| flatten(array)                                 | Converts an array of arrays to a flat array `flatten([[1], [2, 3], [4, 5, 6]]) -> [1, 2, 3, 4, 5, 6]`                                                                                                                                                                            |
| array_length(array, dimension)                 | Returns the length of the array dimension. `array_length([1, 2, 3, 4, 5]) -> 5`                                                                                                                                                                                                  |
| array_ndims(array)                             | Returns the number of dimensions of the array. `array_ndims([[1, 2, 3], [4, 5, 6]]) -> 2`                                                                                                                                                                                        |
| array_pop_front(array)                         | Returns the array without the first element. `array_pop_front([1, 2, 3]) -> [2, 3]`                                                                                                                                                                                              |
| array_pop_back(array)                          | Returns the array without the last element. `array_pop_back([1, 2, 3]) -> [1, 2]`                                                                                                                                                                                                |
| array_position(array, element)                 | Searches for an element in the array, returns first occurrence. `array_position([1, 2, 2, 3, 4], 2) -> 2`                                                                                                                                                                        |
| array_positions(array, element)                | Searches for an element in the array, returns all occurrences. `array_positions([1, 2, 2, 3, 4], 2) -> [2, 3]`                                                                                                                                                                   |
| array_prepend(element, array)                  | Prepends an element to the beginning of an array. `array_prepend(1, [2, 3, 4]) -> [1, 2, 3, 4]`                                                                                                                                                                                  |
| array_repeat(element, count)                   | Returns an array containing element `count` times. `array_repeat(1, 3) -> [1, 1, 1]`                                                                                                                                                                                             |
| array_remove(array, element)                   | Removes the first element from the array equal to the given value. `NULL` elements already in the array are preserved when removing a non-`NULL` value, and `array_remove(array, NULL)` returns `NULL`. `array_remove([1, 2, NULL, 2, 4], 2) -> [1, NULL, 2, 4]`                 |
| array_remove_n(array, element, max)            | Removes the first `max` elements from the array equal to the given value. `NULL` elements already in the array are preserved when removing a non-`NULL` value, and `array_remove_n(array, NULL, max)` returns `NULL`. `array_remove_n([1, 2, NULL, 2, 4], 2, 2) -> [1, NULL, 4]` |
| array_remove_all(array, element)               | Removes all elements from the array equal to the given value. `NULL` elements already in the array are preserved when removing a non-`NULL` value, and `array_remove_all(array, NULL)` returns `NULL`. `array_remove_all([1, 2, NULL, 2, 4], 2) -> [1, NULL, 4]`                 |
| array_replace(array, from, to)                 | Replaces the first occurrence of the specified element with another specified element. `array_replace([1, 2, 2, 3, 2, 1, 4], 2, 5) -> [1, 5, 2, 3, 2, 1, 4]`                                                                                                                     |
| array_replace_n(array, from, to, max)          | Replaces the first `max` occurrences of the specified element with another specified element. `array_replace_n([1, 2, 2, 3, 2, 1, 4], 2, 5, 2) -> [1, 5, 5, 3, 2, 1, 4]`                                                                                                         |
| array_replace_all(array, from, to)             | Replaces all occurrences of the specified element with another specified element. `array_replace_all([1, 2, 2, 3, 2, 1, 4], 2, 5) -> [1, 5, 5, 3, 5, 1, 4]`                                                                                                                      |
| array_slice(array, begin,end)                  | Returns a slice of the array. `array_slice([1, 2, 3, 4, 5, 6, 7, 8], 3, 6) -> [3, 4, 5, 6]`                                                                                                                                                                                      |
| array_slice(array, begin, end, stride)         | Returns a slice of the array with added stride feature. `array_slice([1, 2, 3, 4, 5, 6, 7, 8], 3, 6, 2) -> [3, 5, 6]`                                                                                                                                                            |
| array_to_string(array, delimiter)              | Converts each element to its text representation. `array_to_string([1, 2, 3, 4], ',') -> 1,2,3,4`                                                                                                                                                                                |
| array_intersect(array1, array2)                | Returns an array of the elements in the intersection of array1 and array2. `array_intersect([1, 2, 3, 4], [5, 6, 3, 4]) -> [3, 4]`                                                                                                                                               |
| array_union(array1, array2)                    | Returns an array of the elements in the union of array1 and array2 without duplicates. `array_union([1, 2, 3, 4], [5, 6, 3, 4]) -> [1, 2, 3, 4, 5, 6]`                                                                                                                           |
| array_except(array1, array2)                   | Returns an array of the elements that appear in the first array but not in the second. `array_except([1, 2, 3, 4], [5, 6, 3, 4]) -> [1, 2]`                                                                                                                                      |
| array_resize(array, size, value)               | Resizes the list to contain size elements. Initializes new elements with value or empty if value is not set. `array_resize([1, 2, 3], 5, 0) -> [1, 2, 3, 0, 0]`                                                                                                                  |
| array_sort(array, desc, null_first)            | Returns sorted array. `array_sort([3, 1, 2, 5, 4]) -> [1, 2, 3, 4, 5]`                                                                                                                                                                                                           |
| cardinality(array/map)                         | Returns the total number of elements in the array or map. `cardinality([[1, 2, 3], [4, 5, 6]]) -> 6`                                                                                                                                                                             |
| make_array(value1, [value2 [, ...]])           | Returns an Arrow array using the specified input expressions. `make_array(1, 2, 3) -> [1, 2, 3]`                                                                                                                                                                                 |
| range(start [, stop, step])                    | Returns an Arrow array between start and stop with step. `SELECT range(2, 10, 3) -> [2, 5, 8]`                                                                                                                                                                                   |
| string_to_array(array, delimiter, null_string) | Splits a `string` based on a `delimiter` and returns an array of parts. Any parts matching the optional `null_string` will be replaced with `NULL`. `string_to_array('abc#def#ghi', '#', ' ') -> ['abc', 'def', 'ghi']`                                                          |
| trim_array(array, n)                           | Deprecated                                                                                                                                                                                                                                                                       |

## Regular Expressions

| Syntax         | Description                                                                   |
| -------------- | ----------------------------------------------------------------------------- |
| regexp_match   | Matches a regular expression against a string and returns matched substrings. |
| regexp_replace | Replaces strings that match a regular expression                              |

## Temporal Expressions

| Syntax               | Description                                            |
| -------------------- | ------------------------------------------------------ |
| date_part            | Extracts a subfield from the date.                     |
| date_trunc           | Truncates the date to a specified level of precision.  |
| from_unixtime        | Returns the unix time in format.                       |
| to_timestamp         | Converts a string to a `Timestamp(_, _)`               |
| to_timestamp_millis  | Converts a string to a `Timestamp(Milliseconds, None)` |
| to_timestamp_micros  | Converts a string to a `Timestamp(Microseconds, None)` |
| to_timestamp_seconds | Converts a string to a `Timestamp(Seconds, None)`      |
| now()                | Returns current time.                                  |

## Other Expressions

| Syntax                       | Description                                                                                                |
| ---------------------------- | ---------------------------------------------------------------------------------------------------------- |
| array([value1, ...])         | Returns an array of fixed size with each argument (`[value1, ...]`) on it.                                 |
| in_list(expr, list, negated) | Returns `true` if (`expr`) belongs or not belongs (`negated`) to a list (`list`), otherwise returns false. |
| random()                     | Returns a random value from 0 (inclusive) to 1 (exclusive).                                                |
| sha224(text)                 | Computes the SHA224 hash of the argument (`text`).                                                         |
| sha256(text)                 | Computes the SHA256 hash of the argument (`text`).                                                         |
| sha384(text)                 | Computes the SHA384 hash of the argument (`text`).                                                         |
| sha512(text)                 | Computes the SHA512 hash of the argument (`text`).                                                         |
| to_hex(integer)              | Converts the integer (`integer`) to the corresponding hexadecimal string.                                  |

## Aggregate Functions

| Syntax                                                                          | Description                                                                                                                                              |
| ------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------- |
| avg(expr)                                                                       | Calculates the average value for `expr`.                                                                                                                 |
| avg_distinct(expr)                                                              | Creates an expression to represent the avg(distinct) aggregate function                                                                                  |
| approx_distinct(expr)                                                           | Calculates an approximate count of the number of distinct values for `expr`.                                                                             |
| approx_median(expr)                                                             | Calculates an approximation of the median for `expr`.                                                                                                    |
| approx_percentile_cont(expr, percentile [, centroids])                          | Calculates an approximation of the specified `percentile` for `expr`. Optional `centroids` parameter controls accuracy (default: 100).                   |
| approx_percentile_cont_with_weight(expr, weight_expr, percentile [, centroids]) | Calculates an approximation of the specified `percentile` for `expr` and `weight_expr`. Optional `centroids` parameter controls accuracy (default: 100). |
| bit_and(expr)                                                                   | Computes the bitwise AND of all non-null input values for `expr`.                                                                                        |
| bit_or(expr)                                                                    | Computes the bitwise OR of all non-null input values for `expr`.                                                                                         |
| bit_xor(expr)                                                                   | Computes the bitwise exclusive OR of all non-null input values for `expr`.                                                                               |
| bool_and(expr)                                                                  | Returns true if all non-null input values (`expr`) are true, otherwise false.                                                                            |
| bool_or(expr)                                                                   | Returns true if any non-null input value (`expr`) is true, otherwise false.                                                                              |
| count(expr)                                                                     | Returns the number of rows for `expr`.                                                                                                                   |
| count_distinct(expr)                                                            | Creates an expression to represent the count(distinct) aggregate function                                                                                |
| cube(exprs)                                                                     | Creates a grouping set for all combination of `exprs`                                                                                                    |
| grouping_set(exprs)                                                             | Create a grouping set.                                                                                                                                   |
| max(expr)                                                                       | Finds the maximum value of `expr`.                                                                                                                       |
| median(expr)                                                                    | Calculates the median of `expr`.                                                                                                                         |
| min(expr)                                                                       | Finds the minimum value of `expr`.                                                                                                                       |
| rollup(exprs)                                                                   | Creates a grouping set for rollup sets.                                                                                                                  |
| sum(expr)                                                                       | Calculates the sum of `expr`.                                                                                                                            |
| sum_distinct(expr)                                                              | Creates an expression to represent the sum(distinct) aggregate function                                                                                  |

## Aggregate Function Builder

You can also use the `ExprFunctionExt` trait to more easily build Aggregate arguments `Expr`.

See `datafusion-examples/examples/query_planning/expr_api.rs` for example usage.

| Syntax                                                                  | Equivalent to                       |
| ----------------------------------------------------------------------- | ----------------------------------- |
| first_value_udaf.call(vec![expr]).order_by(vec![expr]).build().unwrap() | first_value(expr, Some(vec![expr])) |

## Subquery Expressions

| Syntax          | Description                                                                                   |
| --------------- | --------------------------------------------------------------------------------------------- |
| exists          | Creates an `EXISTS` subquery expression                                                       |
| in_subquery     | `df1.filter(in_subquery(col("foo"), df2))?` is the equivalent of the SQL `WHERE foo IN <df2>` |
| not_exists      | Creates a `NOT EXISTS` subquery expression                                                    |
| not_in_subquery | Creates a `NOT IN` subquery expression                                                        |
| scalar_subquery | Creates a scalar subquery expression                                                          |

## User-Defined Function Expressions

| Syntax      | Description                                                               |
| ----------- | ------------------------------------------------------------------------- |
| create_udf  | Creates a new UDF with a specific signature and specific return type.     |
| create_udaf | Creates a new UDAF with a specific signature, state type and return type. |
