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;
