UNION with multiple tables

The following query performs a union on three tables. The maximum number of unions depends on the practicality of the application and any memory limitations.

Figure 1. Query

SELECT stock_num, manu_code FROM stock
   WHERE unit_price > 600.00
UNION ALL
SELECT stock_num, manu_code FROM catalog
   WHERE catalog_num = 10025
UNION ALL
SELECT stock_num, manu_code FROM items
   WHERE quantity = 10
   ORDER BY 2;

The query selects items where the unit_price in the stock table is greater than $600, the catalog_num in the catalog table is 10025, or the quantity in the items table is 10; and the query orders the data by manu_code. The result shows the return values.

Figure 2. Query result

stock_num manu_code

        5 ANZ
        9 ANZ
        8 ANZ
        4 HSK
        1 HSK
      203 NKL
        5 NRG
      106 PRC
      113 SHM