MYsql 之單標查詢.

http://www.cnblogs.com/wangfengming/articles/8064956.html

 

3.數據操做

    1.增
        INSERT into t2(name,age) VALUES('小三',11); -- 指定字段插入

        INSERT into t2 VALUES('鳳',13,2.5); -- 整表字段插入

        INSERT into t2 VALUES('鳳',13,2.5),('鳳',13,2.5),('鳳',13,2.5),('鳳',13,2.5),('鳳',13,2.5);
        --插入多條
        insert into t1 SELECT id,name from t2; -- 複製表數據
    2.刪
        delete from t2 where age = 1113;
    3.改
        update t2 set name ='祝小鳳' , salary = 100 where age =13;
    4.查
        select * from T1;
    
        1.簡單查詢
            -- 查詢全部
            select * from person; 
            --查詢指定字段
            select name,age FROM person;
            -- 別名+字段運算
            select p.name,p.salary,p.salary+p.salary*0.1 as 'sum' from person as p
            -- 去重複查詢
            select DISTINCT salary,name from person; 
        
        2.條件查詢
            -- 邏輯運算符 < > <= >= != <> =
            -- is null ,is not null
            -- and  OR ()

            SELECT * from person where salary >5000 or ( age <=30 AND NAME ='');
        
        3.區間查詢
            SELECT * FROM person where salary >=5000 and salary<=10000;
            -- 推薦使用 :
            --ps:先後包含
            
            SELECT * FROM person where salary between 5000 and 10000;
        
        4.集合查詢 in not in
            
            SELECT * FROM person where age = 20 or age = 23 or age =30 ;

            SELECT * FROM person where age not in(20,23,30);
            
            
        5.模糊查詢 like
            SELECT * FROM person where name LIKE '%月'; -- 以什麼結尾

            SELECT * FROM person where name LIKE '月%'; -- 以什麼開頭

            SELECT * FROM person where name LIKE '%月%'; -- 包含

            SELECT * FROM person where name LIKE '_l%'; -- "_"表示佔位符
            
            
        6.排序 
            select * from person ORDER BY salary ASC,age desc;

            -- 強制中文[排序
            select * FROM person ORDER BY CONVERT(name USING GBK) ;
    
        7.聚合函數
            select MAX(salary) from person;
            select MIN(salary) from person;
            select AVG(salary) from person;
            select SUM(salary) from person;
            select COUNT(*) from person;

        8.分組查詢   GROUP BY  HAVING
            select count(id),dept_id,avg(salary) from person GROUP BY dept_id HAVING avg(salary) >=5000 ;
             where 與 having區別:
            #執行優先級從高到低：where > group by > having 
            #1. Where 發生在分組group by以前，於是Where中能夠有任意字段，可是絕對不能使用聚合函數。
            #2. Having發生在分組group by以後，於是Having中能夠使用分組的字段，沒法直接取到其餘字段,能夠使用聚合函數
        
        9.分頁查詢 LIMIT
            SELECT * FROM person LIMIT 2,2

        10.正則表達式
            SELECT * FROM person where name REGEXP '^a';
            
            SELECT * FROM person where name REGEXP 'n$';

            SELECT * FROM person where name REGEXP '.a';

            SELECT * FROM person where name REGEXP '[a,e,n]';

            SELECT * FROM person where name REGEXP '[^alex]';

            SELECT * FROM person where name REGEXP 'a|e';

            SELECT * FROM person where name REGEXP '^w.*i$';


        11. SQL 語句關鍵字的執行順序
            
            執行順序: FROM -> WHERE -> GROUP BY -> HAVING -> SELECT -> ORDER BY ->limit