【MYSQL】语法复习

-- 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;

DROP TABLE T_School;

-- 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);

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

-- 条件删除
DELETE FROM T_User WHERE Id=3;

-- 重置表格，自增主键重新计算
TRUNCATE TABLE T_User;

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

-- 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'

-- 统计行数
SELECT COUNT(1) FROM T_User;

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

SELECT
    GROUP_CONCAT(Name)
FROM T_User
LIMIT 10;

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

//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;

//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;

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

SELECT
    GROUP_CONCAT( CONCAT( CreateBy, ':', Remark ) ) 
FROM
    book 
GROUP BY
    `Name`