Question

Assume 3 tables:

• Table 1 has information about a product’s price (e.g. the base price)
• Table 2 has information about a product’s additional price factors (e.g. taxes, discounts, etc.)
• Table 3 has flags indicating if Table 1 or Table 2 or both tables should be used in computing the product’s total price

Is it possible in MySQL to compute the sum in this situation? If so, some guidance on the query would be appreciated.

Answer 1

SELECT SUM(CASE (SELECT flag FROM table3) 
           WHEN onlyTable1 THEN t1.col
           WHEN onlyTable2 THEN t2.col
           ELSE t1.col+t2.col END)

FROM table1 AS t1 JOIN table2 AS t2