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.

The syntax for the coalesce function is:

coalesce( expr1, expr2, ... expr_n )

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.