mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-09-23 18:20:50 +00:00
60 lines
1.8 KiB
Markdown
60 lines
1.8 KiB
Markdown
---
|
|
toc_priority: 38
|
|
toc_title: FUNCTION
|
|
---
|
|
|
|
# CREATE FUNCTION {#create-function}
|
|
|
|
Creates a user defined function from a lambda expression. The expression must consist of function parameters, constants, operators, or other function calls.
|
|
|
|
**Syntax**
|
|
|
|
```sql
|
|
CREATE FUNCTION name 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:
|
|
|
|
```sql
|
|
CREATE FUNCTION linear_equation AS (x, k, b) -> k*x + b;
|
|
SELECT number, linear_equation(number, 2, 1) FROM numbers(3);
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
┌─number─┬─plus(multiply(2, number), 1)─┐
|
|
│ 0 │ 1 │
|
|
│ 1 │ 3 │
|
|
│ 2 │ 5 │
|
|
└────────┴──────────────────────────────┘
|
|
```
|
|
|
|
A [conditional function](../../../sql-reference/functions/conditional-functions.md) is called in a user defined function in the following query:
|
|
|
|
```sql
|
|
CREATE FUNCTION parity_str AS (n) -> if(n % 2, 'odd', 'even');
|
|
SELECT number, parity_str(number) FROM numbers(3);
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
┌─number─┬─if(modulo(number, 2), 'odd', 'even')─┐
|
|
│ 0 │ even │
|
|
│ 1 │ odd │
|
|
│ 2 │ even │
|
|
└────────┴──────────────────────────────────────┘
|
|
```
|