Question

I have a table A with columns (a, b) and a table B with columns (b, c). I want to do the following:

STEP 1: do a   A LEFT OUTER JOIN B ON A.b = B.b
STEP 2: convert all c = NULL in the Joined table to c = <default_value>
STEP 3: SUM(A.a * B.c) over the table I get after STEP 2

Is there a quick way to do this in one compound statement?

Thanks!

Answer 1

You can do the three steps in one query, first LEFT OUTER JOIN and use IFNULL to set the NULL values to a default value, then use SUM:

SELECT
  SUM(A.a + IFNULL(B.c, <default_value>))
FROM A 
LEFT OUTER JOIN B ON A.b = B.b;

SQL Fiddle Demo:

• STEP 1, STEP 2.

• STEP 3.