Standard library

The standard library currently contains commonly used functions that are used in SQL. It’s not yet as broad as we’d like, and we’re very open to expanding it.

Currently s-strings are an escape-hatch for any function that isn’t in our standard library. If we find ourselves using them for something frequently, raise an issue and we’ll add it to the stdlib.

Here’s the source of the current PRQL std:

Note

PRQL 0.9.0 has started supporting different DB implementations for standard library functions. The source is the std.sql.

# The PRQL standard library defines the following functions and transforms.
# The definitions are whitespace insensitive, and have this form:
#
# ```
# let my_func = param1 param2 ...  -> <return_type> body_expr
# ```
#
# Where:
#   * `my_func` is the name of the function
#   * `param1` is the first parameter optionally followed by a type in "< ... >"
#   * `param2` etc. follow the same pattern as param1
#   * `<return_type>` is the type of result wrapped in "< ... >"
#   * `body_expr` defines the function body that creates the result.
#     It can be PRQL code or `internal ...` to indicate internal compiler code.

# Operators

let mul = left right -> <int || float> internal std.mul
let div_i = left right -> <int || float> internal std.div_i
let div_f = left right -> <int || float> internal std.div_f
let mod = left right -> <int || float> internal std.mod
let add = left right -> <int || float || timestamp || date> internal std.add
let sub = left right -> <int || float || timestamp || date> internal std.sub
let eq = left right -> <bool> internal std.eq
let ne = left right -> <bool> internal std.ne
let gt = left right -> <bool> internal std.gt
let lt = left right -> <bool> internal std.lt
let gte = left right -> <bool> internal std.gte
let lte = left right -> <bool> internal std.lte
let and = left<bool> right<bool> -> <bool> internal std.and
let or = left<bool> right<bool> -> <bool> internal std.or
let coalesce = left right -> internal std.coalesce
let regex_search = text pattern -> <bool> internal std.regex_search

let neg = expr<int || float> -> <int || float> internal std.neg
let not = expr<bool> -> <bool> internal std.not

# Types

## Type primitives
type int = int
type float = float
type bool = bool
type text = text
type date = date
type time = time
type timestamp = timestamp
type `func` = func
type anytype = anytype

## Generic array
# TODO: an array of anything, not just nulls
type array = [anytype]

## Scalar
type scalar = int || float || bool || text || date || time || timestamp || null
type tuple = {anytype..}

## Range
type range = {start = scalar, end = scalar}

## Relation (an array of tuples)
type relation = [tuple]

## Transform
type transform = func relation -> relation

# Functions

## Relational transforms
let from = func
  `default_db.source` <relation>
  -> <relation> source

let select = func
  columns <anytype>
  tbl <relation>
  -> <relation> internal select

let filter = func
  condition <bool>
  tbl <relation>
  -> <relation> internal filter

let derive = func
  columns <anytype>
  tbl <relation>
  -> <relation> internal derive

let aggregate = func
  columns <anytype>
  tbl <relation>
  -> <relation> internal aggregate

let sort = func
  by <anytype>
  tbl <relation>
  -> <relation> internal sort

let take = func
  expr <anytype>
  tbl <relation>
  -> <relation> internal take

let join = func
  `default_db.with` <relation>
  condition <bool>
  `noresolve.side`:inner
  tbl <relation>
  -> <relation> internal join

let group = func
  by<scalar || tuple>
  pipeline <transform>
  tbl <relation>
  -> <relation> internal group

let window = func
  rows:0..-1
  range:0..-1
  expanding <bool>:false
  rolling <int>:0
  pipeline <transform>
  tbl <relation>
  -> <relation> internal window

let append = `default_db.bottom`<relation> top<relation> -> <relation> internal append
let intersect = `default_db.bottom`<relation> top<relation> -> <relation> (
  t = top
  join (b = bottom) (tuple_every (tuple_map _eq (tuple_zip t.* b.*)))
  select t.*
)
let remove = `default_db.bottom`<relation> top<relation> -> <relation> (
  t = top
  join side:left (b = bottom) (tuple_every (tuple_map _eq (tuple_zip t.* b.*)))
  filter (tuple_every (tuple_map _is_null b.*))
  select t.*
)
let loop = func
  pipeline <transform>
  top <relation>
  -> <relation> internal loop

## Aggregate functions
# These return either a scalar when used within `aggregate`, or a column when used anywhere else.

let min = column <array> -> <int || float || null> internal std.min

let max = column <array> -> <int || float || null> internal std.max

let sum = column <array> -> <int || float> internal std.sum

let average = column <array> -> <float || null> internal std.average

let stddev = column <array> -> <float || null> internal std.stddev

let all = column <array> -> <bool> internal std.all

let any = column <array> -> <bool> internal std.any

let concat_array = column <array> -> <text> internal std.concat_array

# Counts number of items in the column.
# Note that the count will include null values.
let count = column<array> -> <int> internal count

# Deprecated in favour of filterning input to the [std.count] function (not yet implemented).
@{deprecated}
let count_distinct = column <array> -> internal std.count_distinct

## Window functions
let lag =   offset <int>    column <array> -> internal std.lag
let lead =  offset <int>    column <array> -> internal std.lead
let first      = column <array> -> internal std.first
let last       = column <array> -> internal std.last
let rank       = column <array> -> internal std.rank
let rank_dense = column <array> -> internal std.rank_dense
let row_number = column <array> -> internal row_number

# Mathematical functions
module math {
  let abs = column -> <int || float> internal std.math.abs
  let floor = column -> <int> internal std.math.floor
  let ceil = column -> <int> internal std.math.ceil
  let pi = -> <float> internal std.math.pi
  let exp = column -> <int || float> internal std.math.exp
  let ln = column -> <int || float> internal std.math.ln
  let log10 = column -> <int || float> internal std.math.log10
  let log = base<int || float> column -> <int || float> internal std.math.log
  let sqrt = column -> <int || float> internal std.math.sqrt
  let degrees = column -> <int || float> internal std.math.degrees
  let radians = column -> <int || float> internal std.math.radians
  let cos = column -> <int || float> internal std.math.cos
  let acos = column -> <int || float> internal std.math.acos
  let sin = column -> <int || float> internal std.math.sin
  let asin = column -> <int || float> internal std.math.asin
  let tan = column -> <int || float> internal std.math.tan
  let atan = column -> <int || float> internal std.math.atan
  let pow = exponent<int || float> column -> <int || float> internal std.math.pow
  let round = n_digits column -> <scalar> internal std.math.round
}

## Misc functions
let as = `noresolve.type` column -> <scalar> internal std.as
let in = pattern value -> <bool> internal in

## Tuple functions
let tuple_every = func list -> <bool> internal tuple_every
let tuple_map = func fn <func> list -> internal tuple_map
let tuple_zip = func a b -> internal tuple_zip
let _eq = func a -> internal _eq
let _is_null = func a -> _param.a == null

## Misc
let from_text = input<text> `noresolve.format`:csv -> <relation> internal from_text

## Text functions
module text {
  let lower = column -> <text> internal std.text.lower
  let upper = column -> <text> internal std.text.upper
  let ltrim = column -> <text> internal std.text.ltrim
  let rtrim = column -> <text> internal std.text.rtrim
  let trim = column -> <text> internal std.text.trim
  let length = column -> <int> internal std.text.length
  let extract = offset<int> length<int> column -> <text> internal std.text.extract
  let replace = pattern<text> replacement<text> column -> <text> internal std.text.replace
  let starts_with = prefix<text> column -> <bool> internal std.text.starts_with
  let contains = substr<text> column -> <bool> internal std.text.contains
  let ends_with = suffix<text> column -> <bool> internal std.text.ends_with
}

## Date functions
module date {
  let to_text = format<text> column -> <text> internal std.date.to_text
}

## File-reading functions, primarily for DuckDB
let read_parquet = source<text> -> <relation> internal std.read_parquet
let read_csv = source<text> -> <relation> internal std.read_csv


## PRQL compiler functions
module `prql` {
  let version = -> <text> internal prql_version
}

# Deprecated, will be removed in 0.12.0
let prql_version = -> <text> internal prql_version

And a couple of examples:

PRQL

from employees
derive {
  gross_salary = (salary + payroll_tax | as int),
  gross_salary_rounded = (gross_salary | math.round 0),
  time = s"NOW()",  # an s-string, given no `now` function exists in PRQL
}

SQL

SELECT
  *,
  CAST(salary + payroll_tax AS int) AS gross_salary,
  ROUND(CAST(salary + payroll_tax AS int), 0) AS gross_salary_rounded,
  NOW() AS time
FROM
  employees

Example of different implementations of division and integer division:

PRQL

prql target:sql.sqlite

from [{x = 13, y = 5}]
select {
  quotient = x / y,
  int_quotient = x // y,
}

SQL

WITH table_0 AS (
  SELECT
    13 AS x,
    5 AS y
)
SELECT
  (x * 1.0 / y) AS quotient,
  ROUND(ABS(x / y) - 0.5) * SIGN(x) * SIGN(y) AS int_quotient
FROM
  table_0

PRQL

prql target:sql.mysql

from [{x = 13, y = 5}]
select {
  quotient = x / y,
  int_quotient = x // y,
}

SQL

WITH table_0 AS (
  SELECT
    13 AS x,
    5 AS y
)
SELECT
  (x / y) AS quotient,
  (x DIV y) AS int_quotient
FROM
  table_0