urQL/docs/in-progress/ref-ch08-functions.md

Functions

IMPORTANT NOTE: the design of functions is still on-going. Nothing is implemented in the parser and take the following as preliminary design work.

Urql has two kinds of functions.

Scalar functions take one or more columns as parameters from a single intermediary data row and return a single scalar value. Scalar functions must be declared after the CTEs and FROM clauses and before the SELECT clause. The user-assigned scalar name may be used in any predicate or SELECT clause.

Aggregate functions operate on a single column of intermediary data rows. They are always declared inline in a SELECT clause or HAVING predicate by the function name, no space, open and close parenthesis which contain parameters specific to the function including the intermediary data column.

Boolean Functions

Boolean funtions can be Scalar or Aggregate and depending on their context must follow rules for either type.

If <expression> is of loobean type (%.y, %.n) normal boolean evaluation proceeds. Evaluation of any other type evaluates as boolean TRUE unless EXISTS <expression> evaluates as FALSE.

AND ::=
  AND(<expression 1>, ..., <expression n>)

OR ::=
  OR(<expression 1>, ..., <expression n>)

XOR ::=
  XOR(<expression 1>, <expression 2>)

NOT ::=
  NOT(<expression)

Scalar Functions

<expression> many be another scalar function, but not aggregate functions.

arithmetic operators

<addition> ::= 
    <expression> + <expression>

<subtraction> ::=
  <expression> - <expression>

<multiplication> ::=
  <expression> * <expression>

<division> ::=
  <expression> / <expression>

<modulo> ::=
  <expression> % <expression>

Returns the integer remainder of a division.

<negation> ::=
  NOT <expression>

NOT (-4) → 4

<exponentiation> ::=
  <expression> ^ <expression>

2 ^ 3 → 8

Unlike typical mathematical practice, multiple uses of ^ will associate left to right by default:

2 ^ 3 ^ 3 → 512

2 ^ (3 ^ 3) → 134217728

bitwise operators

<bitwise AND> ::=
  <expression> & <expression>

91 & 15 → 11

<bitwise OR> ::=
  <expression> | <expression>

32 | 3 → 35

<bitwise Exclusive OR> ::=
  <expression> # <expression>

17 # 5 → 20

<bitwise NOT> ::=
  _ <expression>

_ 1 → -2

<bitwise shift left> ::=
  <expression> << @ud

1 << 4 → 16

(Shift right)

<bitwise shift right> ::=
  <expression> >> @ud

8 >> 2 → 2

predicate

<predicate> ::=
  <predicate>

A scalar returning a predicate follows the same construction rules as a WHERE predicate.

(misc scalars) https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/appendix-e-scalar-functions?view=sql-server-ver16 https://www.postgresql.org/docs/14/functions.html

string scalars

https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/string-functions?view=sql-server-ver16 https://www.postgresql.org/docs/14/functions-string.html https://www.postgresql.org/docs/15/functions-binarystring.html https://www.postgresql.org/docs/15/functions-bitstring.html

numeric scalars

https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/numeric-functions?view=sql-server-ver16 https://www.postgresql.org/docs/15/functions-math.html

date scalars

https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/time-date-and-interval-functions?view=sql-server-ver16 https://www.postgresql.org/docs/15/functions-datetime.html

conversion and casting

https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/explicit-data-type-conversion-function?view=sql-server-ver16 https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/sql-92-cast-function?view=sql-server-ver16 https://www.postgresql.org/docs/14/functions-formatting.html

Aggregate Functions

<expression> many be a scalar function or another aggregate function.

https://learn.microsoft.com/en-us/sql/t-sql/functions/aggregate-functions-transact-sql?view=sql-server-ver16 https://www.postgresql.org/docs/15/functions-aggregate.html