CREATE FUNCTION -user defined function (UDF)
Creates a user defined function (UDF) from a lambda expression. The expression must consist of function parameters, constants, operators, or other function calls.
Syntax
CREATE FUNCTION name [ON CLUSTER cluster] AS (parameter0, ...) -> expression
A function can have an arbitrary number of parameters.
There are a few restrictions:
- The name of a function must be unique among user defined and system functions.
- Recursive functions are not allowed.
- All variables used by a function must be specified in its parameter list.
If any restriction is violated then an exception is raised.
Example
Query:
CREATE FUNCTION linear_equation AS (x, k, b) -> k*x + b;
SELECT number, linear_equation(number, 2, 1) FROM numbers(3);
Result:
┌─number─┬─plus(multiply(2, number), 1)─┐
│ 0 │ 1 │
│ 1 │ 3 │
│ 2 │ 5 │
└────────┴──────────────────────────────┘
A conditional function is called in a user defined function in the following query:
CREATE FUNCTION parity_str AS (n) -> if(n % 2, 'odd', 'even');
SELECT number, parity_str(number) FROM numbers(3);
Result:
┌─number─┬─if(modulo(number, 2), 'odd', 'even')─┐
│ 0 │ even │
│ 1 │ odd │
│ 2 │ even │
└────────┴──────────────────────────────────────┘