In Redshift database, COALESCE is the alias for NVL function. Both NVL and COALESCE return the same output.
NVL returns the first non-null value in the list of expressions passed to the function.
Syntax:
SELECT NVL(value1, value2, value3, ..) from table1; SELECT COALESCE(value1, value2, value3, ..) from table1;
Returns value1 if value1 is not null
Returns value2 if value1 is null
Returns value3 if both value1 and value2 are null.
COALESCE function is very useful to return a non-null value if the value you’re looking for is null.