MySQL CASE 语句和 PHP if 语句哪个更快?
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与 PHP if 语句相比，MySQL CASE 语句更快。PHP if 语句需要花费太多时间，因为它会加载数据然后进行处理，而 CASE 语句则不会。
让我们首先创建一个表并围绕 MySQL CASE 语句的示例进行操作 −
mysql> create table DemoTable (Value int); Query OK, 0 rows affected (0.70 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable values(100); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable values(500); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(1000); Query OK, 1 row affected (0.13 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+-------+ | Value | +-------+ | 100 | | 500 | | 1000 | +-------+ 3 rows in set (0.00 sec)
以下是 MySQL CASE 语句的查询−
mysql> select Value, case when Value > 500 THEN "It is greater than or equal to 1000" else "It is lower than 1000" end as comparison from DemoTable;
这将产生以下输出 −
+-------+-------------------------------------+ | Value | comparison | +-------+-------------------------------------+ | 100 | It is lower than 1000 | | 500 | It is lower than 1000 | | 1000 | It is greater than or equal to 1000 | +-------+-------------------------------------+ 3 rows in set (0.00 sec)
