SQL常见编程代码汇总

1 简单的内连接问题

Q:

Tab1:(学科表)
NodeID NodeName
1 语文
2 数学
3 英语
....

Tab2:(难度表)
TypeID TypeName
1 易
2 较易
3 中
4 较难
5 难

Tab3:(试题表)
QuesID NodeID TypeID
1 1 2
2 1 3
3 2 3
4 2 1
5 3 5
...

要求统计结果：（统计每个学科下每种题型的个数）

易 较易 中 较难 难
语文 0 1 1 0 0
数学 1 0 1 0 0
英语 0 0 0 0 1
...
A:

CREATE TABLE Tab1(NodeID NVARCHAR(2) NOT NULL,NodeName NVARCHAR(20) NOT NULL)
INSERT INTO Tab1(NodeID,NodeName)
SELECT '1','语文' UNION ALL
SELECT '2','数学' UNION ALL
SELECT '3','英语'

CREATE TABLE Tab2(TypeID NVARCHAR(2) NOT NULL,TypeName NVARCHAR(20) NOT NULL)
INSERT INTO Tab2(TypeID,TypeName)
SELECT '1','易' UNION ALL
SELECT '2','较易' UNION ALL
SELECT '3','中' UNION ALL
SELECT '4','较难' UNION ALL
SELECT '5','难'

CREATE TABLE Tab3(QuesID int identity(1,1),NodeID NVARCHAR(2) NOT NULL,TypeID NVARCHAR(2) NOT NULL)
INSERT INTO Tab3(NodeID,TypeID)
SELECT '1','2' UNION ALL
SELECT '1','3' UNION ALL
SELECT '2','3' UNION ALL
SELECT '2','1' UNION ALL
SELECT '3','5'

SELECT 科目=c.NodeName,
易 =SUM(CASE a.TypeID WHEN 1 THEN 1 ELSE 0 END ),
较易=SUM(CASE a.TypeID WHEN 2 THEN 1 ELSE 0 END ),
中 =SUM(CASE a.TypeID WHEN 3 THEN 1 ELSE 0 END ),
较难=SUM(CASE a.TypeID WHEN 4 THEN 1 ELSE 0 END ),
难 =SUM(CASE a.TypeID WHEN 5 THEN 1 ELSE 0 END )

FROM Tab3 a INNER JOIN Tab2 b ON a.TypeID=b.TypeID INNER JOIN Tab1 c ON a.NodeID=c.NodeID

GROUP BY c.NodeName

DROP Table Tab1,Tab2,Tab3