摘要:
1、by keeping them "independent" and then aggregating their aggregates -- we significantly decreased the amount of processing going on.在写统计个数的SQL语句的过程,我们最好,先把每个union all的子集的结果进行分别的汇总,然后,最终统一进行汇总,例如下面两个语句的写法:A:SELECT COUNT(*) FROM (SELECT NULL FROM test_explan UNION ALL SELECT ... 阅读全文