仅当字段包含 null 或 0 时才更新 MySQL 字段?
mysqlmysqli database更新于 2024/8/11 4:28:17
为此，使用 MySQL IF() 设置条件。让我们首先创建一个表 −
mysql> create table DemoTable1592 -> ( -> StudentMarks int -> ); Query OK, 0 rows affected (0.76 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1592 values(56); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1592 values(NULL); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1592 values(98); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1592 values(0); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1592 values(75); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1592 values(NULL); Query OK, 1 row affected (0.11 sec)
使用 select 语句显示表中的所有记录 −
mysql> select * from DemoTable1592;
这将产生以下输出 −
+--------------+ | StudentMarks | +--------------+ | 56 | | NULL | | 98 | | 0 | | 75 | | NULL | +--------------+ 6 rows in set (0.00 sec)
以下查询仅当字段包含 null 或 0 时才更新该字段 −
mysql> update DemoTable1592 set StudentMarks=if(StudentMarks IS NULL or StudentMarks=0,33,StudentMarks); Query OK, 3 rows affected (0.17 sec) Rows matched: 6 Changed: 3 Warnings: 0
让我们再次检查表记录 −
mysql> select * from DemoTable1592;
这将产生以下输出 −
+--------------+ | StudentMarks | +--------------+ | 56 | | 33 | | 98 | | 33 | | 75 | | 33 | +--------------+ 6 rows in set (0.00 sec)
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