www.5129.net > SQL语句理解 sElECt * From B whErE (sElECt Count...

SQL语句理解 sElECt * From B whErE (sElECt Count...

假设个例子吧:A表 id 姓名 性别 00 aa 女 01 bb 女 02 cc 女 B表 id 姓名 性别 00 aa 女 02 cc 女 03 dd 男 select * from B是执行B表, 当执行id=‘00’时 ,因为select count(1) as num from A where A.ID = B.ID 不等于0 所以运行结果没有第一...

select count(*) from aa where (select * from aa where a=1)错了 select count(*) from aa where a=1 select count(*) from aa where a in (select a from aa where a=1)

Mysql中可以执行,符合mysql规范,默认返回第一条记录的id 但是oracle不能执行,报ORA-00937,所以不符合oracle规范

SELECT SUM ( t.iSum ) as sum FROM ( select count(A.abc) as iSum from A left join B on A.id=B.id where A.abc='1' group by A.abc ); 或者 select count(A.abc) as sum from A left join B on A.id=B.id where A.abc='1'

select a. col1, b.col2 from (select count(id) as col1 from table1) as a, (select count(id) as col2 from table2) as b -------------这样写。

统计在 soft表(也就是a表)里面ID字段与b表里面ID字段相同的记录的条数

select countB)from A group by B order by B SQL语句就可以做了,例检索表格aaa,添加一列“re_num”,显示a列值重复的次数, 次数为表格按a列分组计算记录数: select a,count(a) as 're_num' from aaa group by a, select a1.a2.re_num from aaa ...

一、简单查询语句 1. 查看表结构 SQL>DESC emp; 2. 查询所有列 SQL>SELECT * FROM emp; 3. 查询指定列 SQL>SELECT empmo, ename, mgr FROM emp; SQL>SELECT DISTINCT mgr FROM emp; 只显示结果不同的项 4. 查询指定行 SQL>SELECT * FROM emp WHE...

String s = "SELECT e.*,d.dname FROM emp e LEFT JOIN dept d ON d.did=e.did WHERE 1=1"; String regex = ".*(FROM.*)$"; String result = s.replaceAll(regex, "SELECT count(*) $1"); System.out.println(result); .表示任意字符,*表示0到...

select count(1) from (select * from Test) as t; 或者 select count(1) from Test;

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