1、t_test1表
t_test2表
2、查询需求:求t_test1.num与t_test2.amount之和
方法一:
SELECT SUM(test.num) AS count FROM(SELECT * FROM t_test1 UNION ALL SELECT * FROM t_test2) AS test;
方法二:
SELECT SUM(test.num) AS count FROM(SELECT t_test1.num FROM t_test1 UNION ALL SELECT t_test2.amount FROM t_test2) AS test;