MySQL 一次计算多个列或单独的事务

Question

我有一个每天的 cron，它计算特定列的非 null 和非空字符串行的数量，例如:

SELECT count(first_name) FROM users WHERE first_name IS NOT NULL and first_name IS != ''
SELECT count(last_name) FROM users WHERE last_name IS NOT NULL and first_name IS != ''

如果我在一次 MySQL 调用中执行此操作，性能会得到改善吗？

Answer 1

对 1 个查询使用 CASE 条件

SELECT SUM(CASE WHEN first_name IS NOT NULL and first_name != '' THEN 1 ELSE 0 END),
       SUM(CASE WHEN last_name IS NOT NULL and last_name != '' THEN 1 ELSE 0 END) FROM users