Functions

PostgreSQL User's Guide
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# Chapter 5. Functions

> Describes the built-in functions available in Postgres.

Many data types have functions available for conversion to other related types. In addition, there are some type-specific functions. Some functions are also available through operators and may be documented as operators only.

# SQL Functions

SQL functions are constructs defined by the SQL92 standard which have function-like syntax but which can not be implemented as simple functions.

Table 5-1. SQL Functions

Function | Returns | Description | Example
--- | --- | --- | ---
COALESCE(`list`) | non-NULL | return first non-NULL value in list | COALESCE(rle, c2 + 5, 0)
NULLIF(`input`,`value`) | `input` or NULL | return NULL if `input` = `value`, else `input` | NULLIF(c1, 'N/A')
CASE WHEN `expr` THEN `expr` [...] ELSE `expr` END | `expr` | return expression for first true WHEN clause | CASE WHEN c1 = 1 THEN 'match' ELSE 'no match' END

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