如果MySQL栏位栏位空白，将其视为NULL？
让我们首先创建一个表-
mysql> create table DemoTable1362
-> (
-> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> ClientName varchar(40)
-> );使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1362(ClientName) values('Chris');
mysql> insert into DemoTable1362(ClientName) values(' ');
mysql> insert into DemoTable1362(ClientName) values('Bob');
mysql> insert into DemoTable1362(ClientName) values(' ');
mysql> insert into DemoTable1362(ClientName) values('David');
mysql> insert into DemoTable1362(ClientName) values(NULL);使用select语句显示表中的所有记录-
mysql> select * from DemoTable1362;
这将产生以下输出-
+----------+------------+ | ClientId | ClientName | +----------+------------+ | 1 | Chris | | 2 | | | 3 | Bob | | 4 | | | 5 | David | | 6 | NULL | +----------+------------+ 6 rows in set (0.00 sec)
以下是将列字段为空的查询，如果该字段为空-
mysql> update DemoTable1362
-> set ClientName=NULL
-> where ClientName='' or length(ClientName)=0;
Rows matched: 2 Changed: 2 Warnings: 0让我们再次检查表记录-
mysql> select * from DemoTable1362;
这将产生以下输出-
+----------+------------+ | ClientId | ClientName | +----------+------------+ | 1 | Chris | | 2 | NULL | | 3 | Bob | | 4 | NULL | | 5 | David | | 6 | NULL | +----------+------------+ 6 rows in set (0.00 sec)