SELECT COUNT(1) ---记录总数 FROM TABLESCORE A WHERE (SELECT COUNT(1) --求记录数 FROM TABLESCORE B WHERE B.CLASS=A.CLASS AND B.SCORE>A.SCORE---与外面的表A对比 班级相同 分数比外面的大 ) <2 ---嵌套语句记录数小于2
sql还能这样写。。最怕这种层次混乱、看似每条记录都要执行一次子程序的sql
不过,用传统的sql2000语法,仅仅是取 每个班级最高2个分数 就很困难了: select class,top 2 distinct score from tb group by class ——语法好像不支持上面的写法
--------------------------------- -- Author: liangCK 小梁 -- Title : 查每个分组前N条记录 -- Date : 2008-11-13 17:19:23 -----------------------------------> 生成测试数据: #T IF OBJECT_ID('tempdb.dbo.#T') IS NOT NULL DROP TABLE #T CREATE TABLE #T (ID VARCHAR(3),GID INT,Author VARCHAR(29),Title VARCHAR(39),Date DATETIME) INSERT INTO #T SELECT '001',1,'邹建','深入浅出SQLServer2005开发管理与应用实例','2008-05-10' UNION ALL SELECT '002',1,'胡百敬','SQLServer2005性能调校','2008-03-22' UNION ALL SELECT '003',1,'格罗夫Groff.J.R.','SQL完全手册','2009-07-01' UNION ALL SELECT '004',1,'KalenDelaney','SQLServer2005技术内幕存储引擎','2008-08-01' UNION ALL SELECT '005',2,'Alex.Kriegel.Boris.M.Trukhnov','SQL宝典','2007-10-05' UNION ALL SELECT '006',2,'飞思科技产品研发中心','SQLServer2000高级管理与开发','2007-09-10' UNION ALL SELECT '007',2,'胡百敬','SQLServer2005数据库开发详解','2008-06-15' UNION ALL SELECT '008',3,'陈浩奎','SQLServer2000存储过程与XML编程','2005-09-01' UNION ALL SELECT '009',3,'赵松涛','SQLServer2005系统管理实录','2008-10-01' UNION ALL SELECT '010',3,'黄占涛','SQL技术手册','2006-01-01'--SQL查询如下:--按GID分组,查每个分组中Date最新的前2条记录 --1.字段ID唯一时: SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)--2.如果ID不唯一时: SELECT * FROM #T AS T WHERE 2>(SELECT COUNT(*) FROM #T WHERE GID=T.GID AND Date>T.Date)--SQL Server 2005 使用新方法--3.使用ROW_NUMBER()进行排位分组 SELECT ID,GID,Author,Title,Date FROM ( SELECT rid=ROW_NUMBER() OVER(PARTITION BY GID ORDER BY Date DESC),* FROM #T ) AS T WHERE rid<=2--4.使用APPLY SELECT DISTINCT b.* FROM #T AS a CROSS APPLY ( SELECT TOP(2) * FROM #T WHERE a.GID=GID ORDER BY Date DESC ) AS b --结果 /*ID GID Author Title Date ---- ----------- ----------------------------- --------------------------------------- ----------------------- 003 1 格罗夫Groff.J.R. SQL完全手册 2009-07-01 00:00:00.000 004 1 KalenDelaney SQLServer2005技术内幕存储引擎 2008-08-01 00:00:00.000 005 2 Alex.Kriegel.Boris.M.Trukhnov SQL宝典 2007-10-05 00:00:00.000 007 2 胡百敬 SQLServer2005数据库开发详解 2008-06-15 00:00:00.000 009 3 赵松涛 SQLServer2005系统管理实录 2008-10-01 00:00:00.000 010 3 黄占涛 SQL技术手册 2006-01-01 00:00:00.000(6 行受影响) */
N种方法 还是SQL 2005的好理解
不过,用传统的sql2000语法,仅仅是取 每个班级最高2个分数 就很困难了: select class,top 2 distinct score fs from TABLESCORE group by class order by class,fs desc ——语法好像不支持上面的写法但是每个班级最高1个分数就很简单: select class,max(score) fs from TABLESCORE group by class
class班级,score分数 SELECT COUNT(1) FROM TABLESCORE A WHERE (SELECT COUNT(1) FROM TABLESCORE B WHERE B.CLASS=A.CLASS AND B.SCORE>A.SCORE ---首先这句话的写法是什么原理,根据什么语法来的, ) <2 --这个条件 count(1) 等于10和等于1 它的意义有什么区别吗?,测试后回复, 最后你就理解成,这个语句怎么可以这样写呢,怎么回得出这个效果来解释就可以了, 谢谢~!非常感谢大家回复~!
COUNT(1) ---记录总数
FROM
TABLESCORE A
WHERE
(SELECT
COUNT(1) --求记录数
FROM
TABLESCORE B
WHERE
B.CLASS=A.CLASS AND B.SCORE>A.SCORE---与外面的表A对比 班级相同 分数比外面的大
) <2 ---嵌套语句记录数小于2
select class,top 2 distinct score
from tb
group by class
——语法好像不支持上面的写法
-- Author: liangCK 小梁
-- Title : 查每个分组前N条记录
-- Date : 2008-11-13 17:19:23
-----------------------------------> 生成测试数据: #T
IF OBJECT_ID('tempdb.dbo.#T') IS NOT NULL DROP TABLE #T
CREATE TABLE #T (ID VARCHAR(3),GID INT,Author VARCHAR(29),Title VARCHAR(39),Date DATETIME)
INSERT INTO #T
SELECT '001',1,'邹建','深入浅出SQLServer2005开发管理与应用实例','2008-05-10' UNION ALL
SELECT '002',1,'胡百敬','SQLServer2005性能调校','2008-03-22' UNION ALL
SELECT '003',1,'格罗夫Groff.J.R.','SQL完全手册','2009-07-01' UNION ALL
SELECT '004',1,'KalenDelaney','SQLServer2005技术内幕存储引擎','2008-08-01' UNION ALL
SELECT '005',2,'Alex.Kriegel.Boris.M.Trukhnov','SQL宝典','2007-10-05' UNION ALL
SELECT '006',2,'飞思科技产品研发中心','SQLServer2000高级管理与开发','2007-09-10' UNION ALL
SELECT '007',2,'胡百敬','SQLServer2005数据库开发详解','2008-06-15' UNION ALL
SELECT '008',3,'陈浩奎','SQLServer2000存储过程与XML编程','2005-09-01' UNION ALL
SELECT '009',3,'赵松涛','SQLServer2005系统管理实录','2008-10-01' UNION ALL
SELECT '010',3,'黄占涛','SQL技术手册','2006-01-01'--SQL查询如下:--按GID分组,查每个分组中Date最新的前2条记录
--1.字段ID唯一时:
SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)--2.如果ID不唯一时:
SELECT * FROM #T AS T WHERE 2>(SELECT COUNT(*) FROM #T WHERE GID=T.GID AND Date>T.Date)--SQL Server 2005 使用新方法--3.使用ROW_NUMBER()进行排位分组
SELECT ID,GID,Author,Title,Date
FROM
(
SELECT rid=ROW_NUMBER() OVER(PARTITION BY GID ORDER BY Date DESC),*
FROM #T
) AS T
WHERE rid<=2--4.使用APPLY
SELECT DISTINCT b.*
FROM #T AS a
CROSS APPLY
(
SELECT TOP(2) * FROM #T WHERE a.GID=GID ORDER BY Date DESC
) AS b
--结果
/*ID GID Author Title Date
---- ----------- ----------------------------- --------------------------------------- -----------------------
003 1 格罗夫Groff.J.R. SQL完全手册 2009-07-01 00:00:00.000
004 1 KalenDelaney SQLServer2005技术内幕存储引擎 2008-08-01 00:00:00.000
005 2 Alex.Kriegel.Boris.M.Trukhnov SQL宝典 2007-10-05 00:00:00.000
007 2 胡百敬 SQLServer2005数据库开发详解 2008-06-15 00:00:00.000
009 3 赵松涛 SQLServer2005系统管理实录 2008-10-01 00:00:00.000
010 3 黄占涛 SQL技术手册 2006-01-01 00:00:00.000(6 行受影响)
*/
select class,top 2 distinct score fs
from TABLESCORE
group by class
order by class,fs desc
——语法好像不支持上面的写法但是每个班级最高1个分数就很简单:
select class,max(score) fs
from TABLESCORE
group by class
(SELECT COUNT(1) FROM TABLESCORE
B WHERE B.CLASS=A.CLASS AND B.SCORE>A.SCORE ---首先这句话的写法是什么原理,根据什么语法来的,
) <2 --这个条件 count(1) 等于10和等于1 它的意义有什么区别吗?,测试后回复,
最后你就理解成,这个语句怎么可以这样写呢,怎么回得出这个效果来解释就可以了,
谢谢~!非常感谢大家回复~!