In Oracle/PLSQL, the coalesce function returns the first non-null expression in the list. If all expressions evaluate to null, then the coalesce function will return null.
Syntax
The syntax for the coalesce function is:
coalesce( expr1, expr2, ... expr_n )
expr1 to expr_n are the expressions to test for non-null values.
Applies To
For Example
You could use the coalesce function in an SQL statement as follows:
SELECT coalesce( address1, address2, address3 ) result
FROM suppliers;
The above coalesce statement is equivalent to the following IF-THEN-ELSE statement:
IF address1 is not null THEN
result := address1;
ELSIF address2 is not null THEN
result := address2;
ELSIF address3 is not null THEN
result := address3;
ELSE
result := null;
END IF;
The coalesce function will compare each value, one by one.