在 MySQL 中为每列值选择三个具有固定字符数的随机记录
mysqlmysqli database
为此，您可以使用 CHAR_LENGTH()。对于随机记录，请使用 RAND()。让我们首先创建一个表 −
mysql> create table DemoTable (Subject text); Query OK, 0 rows affected (0.61 sec)
示例
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable values('C');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('MySQL');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Java');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('MongoDB');
Query OK, 1 row affected (0.59 sec)
mysql> insert into DemoTable values('RubyOnRails');
Query OK, 1 row affected (0.25 sec)
mysql> insert into DemoTable values('C++');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Python');
Query OK, 1 row affected (0.20 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
输出
+-------------+ | Subject | +-------------+ | C | | MySQL | | Java | | MongoDB | | RubyOnRails | | C++ | | Python | +-------------+ 7 rows in set (0.00 sec)
以下查询选择 3 条随机记录，每条记录具有固定的字符数 −
mysql> select *from (select *from DemoTable WHERE CHAR_LENGTH(Subject) = 7 ORDER BY RAND() LIMIT 1 ) tbl UNION (select *from DemoTable WHERE CHAR_LENGTH(Subject) = 11 ORDER BY RAND() LIMIT 1 ) UNION (select *from DemoTable WHERE CHAR_LENGTH(Subject) = 5 ORDER BY RAND() LIMIT 1 );
输出
+-------------+ | Subject | +-------------+ | MongoDB | | RubyOnRails | | MySQL | +-------------+ 3 rows in set (0.04 sec
