The Firebird 5.0 Language Reference | Conditional Functions

Procedural SQL (PSQL) StatementsAggregate Functions

`NULLIF()`

Conditional NULL function

Result type

Depends on input

Syntax

NULLIF (<exp1>, <exp2>)

Table 1. `NULLIF` Function Parameters
Parameter	Description
exp1	An expression
exp2	Another expression of a data type compatible with exp1

NULLIF returns the value of the first argument, unless it is equal to the second.In that case, NULL is returned.

`NULLIF` Example

select avg( nullif(Weight, -1) ) from FatPeople

This will return the average weight of the persons listed in FatPeople, excluding those having a weight of -1, since AVG skips NULL data.Presumably, -1 indicates “weight unknown” in this table.A plain AVG(Weight) would include the -1 weights, thus skewing the result.

NULLIF()

NULLIF()

NULLIF Example

`NULLIF()`

`NULLIF` Example