where條件表達式
--統計函數

復制代碼 代碼如下:

Select count(1) from student;

復制代碼 代碼如下:

select count(*) from student where realName like '張%';

復制代碼 代碼如下:

select count(*) from student where realName like '張_';

復制代碼 代碼如下:

select count(*) from student where home like '%杭州%';

復制代碼 代碼如下:

select realName,year(now())-year(birthday) as age from student;

復制代碼 代碼如下:

select realName from student where year(birthday)>='1990';

復制代碼 代碼如下:

select realName from student where year(birthday)<='1990' and year(birthday)>='1987';
select * from student where year(birthday) between '1987' and '1990';

復制代碼 代碼如下:

select sex,count(*) from student group by sex;

復制代碼 代碼如下:

select realName,blood from student where blood in('B','O'); 

按子查詢返回的記錄行數區分，可分為單行子查詢和多行子查詢；

復制代碼 代碼如下:

select * from emp where sal>(       select sal from emp where ename='ALLEN‘ or ename =‘KING')

A.子查詢一般先于主語句的運行
B.必須有( )，表示一個整體
C.習慣上把子查詢放在條件的右邊
多行子查詢：some,any,all

連接語句(應用于多表查詢)
包括：內聯，外聯(左外連和右外聯)
內聯(inner join)：把兩張表相匹配的行查詢出來。

--查詢每個學生的各科成績，顯示“姓名”“課程名”“分數”三列

復制代碼 代碼如下:

select a.realname,c.courseName,b.score from stu_student as a inner join stu_score as b on a.sid=b.sid inner join stu_course c on b.cid=c.cid

復制代碼 代碼如下:

select a.realname,c.courseName,b.score from student a,score b,course c where a.sid=b.sid and c.cid=b.cid

復制代碼 代碼如下:

select a.realname,b.score from stu_student as a left outer join stu_score as b on a.sid=b.sid