查询SQL

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单表查询：

常规查询：

SELECT 列名 From 表名

去重式查询： DISTINCT

SELECT DISTINCT Sno FROM SC;

比较式查询：BETWEEN = <

SELECT Sname FROM Student WHERE Sage<20;
SELECT Sname FROM Student WHERE Sage Between 20 AND 40;
SELECT NAME FROM Student WHERE Sdept='CS' AND age<20;

字符串匹配式查询：% _

SELECT NAME FROM Student WHERE NAME LIKE '欧阳__'

排序式查询：ORDER BY

SELECT NAME FROM Student WHERE AGE=22 ORDER BY ID;

统计式查询： COUNT(*) ， AVG(ID) ， MAX(ID) ， GROUP BY

SELECT COUNT(*) FROM Student;

SELECT COUNT(DISTANT NAME) FROM Student;

SELECT AVG(ID) FROM Student;

SELECT MAX(ID) FROM Student;

SELECT ID,COUNT(ID) FROM Student GROUP BY ID HAVING COUNT(*)>3;

多表查询：

连接查询：SELECT A.B C.D FROM A,C WHERE ....

SELECT STUDENT.*,SC.* FROM STUDENT,SC WHERE STUDENT.Sno=SC.Sno;

嵌套查询： WHERE...IN(SELECT...)

SELECT NAME FROM STUDENT WHERE Sno IN (SELECT Sno FROM SC WHERE Cno='2')

带有EXISTS 谓语的BOOL子查询

SELECT NAME FROM Student WHERE EXISTS (SELECT * FROM SC WHERE Sno=Student.Sno AND Cno='1')

集合查询：

SELECT * FROM Student WHERE Sdept='CS' UNION SELECT * FROM Student WHERE Sage<=19;