Return MAX(Null) as Null in postgresql-CodePudding

I have a scenario where the max function should work as follows in PostgreSQL:

select max(3,null) from table

should return 3

whereas,

select max(null) from table

should return null.

Suggestions are welcomed!

CodePudding user response：

max() is an aggregate that works across rows, not columns.

You are looking for greatest()

select greatest(3,null) from table

CodePudding user response：

You can use values clause to build a list of values and call max aggregate function over it:

select (
    select max(v)
    from (values
        (3),
        (null),
        (t.foo),
        (t.bar)
    ) as x(v)
)
from t