mysql常用操作记录

1，删除多个重复字段的数据

创建表

CREATE TABLE `TEST` (
  `ID` BIGINT(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `CODE` VARCHAR(32) DEFAULT NULL,
  `NAME` VARCHAR(32) DEFAULT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=INNODB AUTO_INCREMENT=20 DEFAULT CHARSET=UTF8;

插入数据

TRUNCATE TABLE `TEST`;
INSERT INTO `TEST`(`ID`,`CODE`,`NAME`) VALUES
(1,'C1','N1'),
(2,'C2','N2'),
(3,'C2','N2'),
(4,'C2','N21'),
(5,'C2','N21'),
(6,'C3','N3'),
(7,'C3','N3'),
(8,'C3','N3'),
(9,'C3','N31'),
(10,'C3','N31'),
(11,'C3','N31'),
(12,'C4','N4'),
(13,'C4','N4'),
(14,'C4','N4'),
(15,'C4','N4'),
(16,'C4','N41'),
(17,'C4','N41'),
(18,'C4','N41'),
(19,'C4','N41');

删除

DELETE FROM `TEST` WHERE `ID` IN(
    SELECT * FROM(
        SELECT `ID` FROM `TEST` WHERE (`CODE`,`NAME`) IN (
            SELECT `CODE`,`NAME` FROM `TEST` GROUP BY `CODE`,`NAME` HAVING COUNT(*)> 1
        )
        AND `ID` NOT IN(
            SELECT MIN(`ID`)FROM `TEST` GROUP BY `CODE`,`NAME` HAVING COUNT(*)> 1
        )
    ) T
);

2.查看和修改编码

A. 查看数据库的字符集方式

– database_name 为数据库名称

SHOW CREATE DATABASE database_name;

B. 查看表的字符集方式
– table_name为表的名称

SHOW CREATE TABLE table_name;

C. 查看字段的字符集方式

– table_name为表名称

SHOW FULL COLUMNS FROM table_name;

修改数据库、表和字段的字符集方式如下
A. 修改数据库的字符集方式

– database_name 为数据库名称
– utf8为目标字符编码

ALTER DATABSE database_name DEFAULT CHARACTER SET utf8;

B. 修改表的字符集方式

– table_name为表的名称
– utf8为目标字符编码

ALTER TABLE table_name DEFAULT CHARACTER SET utf8;

C. 修改字段的字符集方式

– table_name为表的名称
– column_name为字段名称
– varchar(20)为字段的类型
– utf8为目标字符集

ALTER TABLE table_name CHANGE column_name column_name VARCHAR(20) CHARACTER SET utf8;

D. 同时修改表和表中所有字符类型的字段字符集方式

– 例子：alter table user2 convert to character set utf8 collate utf8_general_ci;

ALTER TABLE tbl_name CONVERT TO CHARACTER SET character_name [COLLATE ...]