关于数据库的一些基本操作语句

Posted 2021-12-14 blogngnl

　♦ ♣ 一些常见的数据库操作语句

====== 创建一个表 ======

CREATE TABLE  `test1` (
 `id` INT( 6 ) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
 `name` VARCHAR( 30 ) NOT NULL ,
 `age` VARCHAR( 30 ) NOT NULL ,
 `timestamp` TIMESTAMP NOT NULL
) ENGINE = MYISAM ;



====== 插入新数据 ======

INSERT INTO  `test1` (`id` ,`name` ,`age`)
VALUES (NULL ,  ‘aa‘,  ‘11‘), (NULL ,  ‘dd‘,  ‘12‘);



====== 删除数据 ======

DELETE FROM `test1` WHERE `test1`.`id` = 12;



====== 更新数据 ======

UPDATE  `test1` SET  `age` =  ‘13‘ WHERE  `test1`.`id` =12





1. 查看过滤重复后的数据

SELECT id,  `name` , age, COUNT( 1 ) AS aaa
FROM test1
GROUP BY  `name` , age


2. 查看重复的数据

SELECT id,  `name` , age, COUNT( 1 ) AS c
FROM test1
GROUP BY  `name` , age
HAVING c >1


3.分组数据，从每组里面取出一个最小的id

SELECT MIN( id ) 
FROM test1
GROUP BY name, age


4.删除重复项，只保留一项

DELETE FROM test1 WHERE id NOT IN (
    SELECT temp.min_id
    FROM (
        SELECT MIN( id ) min_id
        FROM test1
        GROUP BY name, age
    ) AS temp
);
SELECT * FROM test1;