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 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.

See also

[fblangref50-scalarfuncs-coalesce], [fblangref50-scalarfuncs-decode], [fblangref50-scalarfuncs-iif], CASE