为MySQL中的每个列值选择三个具有固定字符数的随机记录
为此，您可以使用CHAR_LENGTH()。使用RAND()进行随机记录。让我们首先创建一个表-
create table DemoTable (Subject text);
示例
使用插入命令在表中插入一些记录-
insert into DemoTable values('C');
insert into DemoTable values('MySQL');
insert into DemoTable values('Java');
insert into DemoTable values('MongoDB');
insert into DemoTable values('RubyOnRails');
insert into DemoTable values('C++');
insert into DemoTable values('Python');使用select语句显示表中的所有记录-
select *from DemoTable;
输出结果
+-------------+ | Subject | +-------------+ | C | | MySQL | | Java | | MongoDB | | RubyOnRails | | C++ | | Python | +-------------+ 7 rows in set (0.00 sec)
以下是查询以选择3条随机记录，每个记录的字符数固定-
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 );
输出结果
+-------------+ | Subject | +-------------+ | MongoDB | | RubyOnRails | | MySQL | +-------------+ 3 rows in set (0.04 sec