MYSQL语法复习

Posted 2020-10-27 blackarrow

一、数据类型

截图来源: http://www.runoob.com/mysql/mysql-data-types.html

二、基本语句

1、创建数据表

//主键自增，T_User
CREATE TABLE IF NOT EXISTS `T_User`(
   `Id` INT UNSIGNED AUTO_INCREMENT,
   `Name` VARCHAR(100) NOT NULL,
   `CardNo` VARCHAR(40) NOT NULL,
   `Birthday` DATE,
   PRIMARY KEY ( `Id` )
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

2、删除数据表

DROP TABLE T_School;

3、新增数据

INSERT INTO T_User (Name, CardNo, BirthDay) VALUES(‘大王‘, ‘0001‘, NOW());

4、删除数据

//条件删除
DELETE FROM T_User WHERE Id=3;

//清空表格，自增主键不会重置
DELETE FROM T_User；
//或者，自增主键重置
TRUNCATE TABLE T_User;

5、更新数据

UPDATE T_User SET Name=‘女王‘, CardNo=‘NX_01‘ WHERE Id=4;

6、查询数据

//查询表所有数据
SELECT * FROM T_User;

//条件查询
SELECT * FROM T_User WHERE Id>2 AND Name IS NOT NULL;

//分组
SELECT Name FROM T_User GROUP BY Name;

//排序,默认ASC,顺序
SELECT * FROM T_User ORDER BY Id DESC;

//INNER JOIN（内连接,或等值连接：获取两个表中字段匹配关系的记录。
//LEFT JOIN（左连接：获取左表所有记录，即使右表没有对应匹配的记录。
//RIGHT JOIN（右连接：与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录。
SELECT TU.* FROM T_User TU 
INNRT JOIN T_School TS ON TS.Id = TU.SchoolId
WHERE TS.`LEVEL` = 1;

//UNION ALL: 返回所有结果集，包含重复数据
//UNION DISTINCT: 删除结果集中重复的数据，默认去重
SELECT Id, Name FROM T_User WHERE ClassName=‘三年二班‘
UNION ALL
SELECT Id, Name FROM T_User WHERE ClassName=‘三年五班‘

//统计
SELECT COUNT(1) FROM T_User;

 7、表字段修改

 

//新增字段
ALTER TABLE T_User ADD ClassName VARCHAR(100) NOT NULL;

//删除字段
ALTER TABLE T_User DROP CardNo;

//修改字段数据属性
ALTER TABLE T_User MODIFY Name BIGINT NOT NULL DEFAULT 100;

//修改字段名称
ALTER TABLE T_User CHANGE Name RealName VARCHAR(100);

 

三、其他函数

1、判断

SELECT 
    IF(SEX = 1, ‘男‘, ‘女‘) SEX
FROM T_USER;

2、逗号拼接

SELECT
    GROUP_CONCAT(Name)
FROM T_User
LIMIT 10;

3、判空

SELECT 
    IFNULL(CardNo, ‘0000‘) CardNo
FROM T_User
WHERE Id>10;

4、转换数据类型

//类型转换
SELECT CAST(Id AS CHAR) FROM T_User; 
//拼接个空字符串，隐式转换
SELECT CONCAT(Id,‘‘) FROM T_User;

5、分页及统计行数

//方法一
SELECT
        TAB.*,
        @i Total
FROM
        (SELECT
                (@i := @i + 1) AS RowNum,
                B.* 
            FROM
                book B,
                (SELECT @i := 0) AS it 
        ) TAB
WHERE TAB.RowNum BETWEEN 5 AND 10
//方法二：
SET @i=0;
SELECT
        TAB.*,
        @i Total
FROM
        (SELECT
                (@i := @i + 1) AS RowNum,
                B.* 
            FROM
                book B
        ) TAB
WHERE TAB.RowNum BETWEEN 5 AND 10;
SET @i:=NULL;

6、时间格式转换

//yyyy-MM-dd HH:mm:ss
date_format(Birthday, ‘%Y-%m-%d %H:%i:%s‘)