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Legal Studies仅显示包含空白的相应列的列值的 MySQL 查询
为此，使用 TRIM() 函数。让我们首先创建一个表 −
mysql> create table DemoTable826( FirstName varchar(100), Age int ); Query OK, 0 rows affected (0.60 sec)
使用插入命令在表中插入一些记录。在此，我们已将某些记录的 FirstName 设为空白 −
mysql> insert into DemoTable826 values(' ',24);
Query OK, 1 row affected (0.08 sec)
mysql> insert into DemoTable826 values(' ',22);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable826 values('Chris',26);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable826 values('Robert',27);
Query OK, 1 row affected (0.07 sec)使用 select 语句从表中显示所有记录 −
mysql> select *from DemoTable826 ;
这将生成以下输出 −
+-----------+------+ | FirstName | Age | +-----------+------+ | Adam | 21 | | | 24 | | | 22 | | Chris | 26 | | Robert | 27 | +-----------+------+ 5 rows in set (0.00 sec)
以下是仅显示包含空白的相应列的列值的查询 −
mysql> select *from DemoTable826 where COALESCE(TRIM(FirstName), '') = '';
这将生成以下输出 −
+-----------+------+ | FirstName | Age | +-----------+------+ | | 24 | | | 22 | +-----------+------+ 2 rows in set (0.00 sec)
更新日期：03-Sep-2019
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