mysql 常用语句整理

开发手册：https://dev.mysql.com/doc/refman/8.0/en/information-functions.html

1. 替换某个字段中的部分内容

SET @oldlink1 = 'http://192.168.100.66';
SET @newlink1 = 'www.baidu.com';

UPDATE Test1
SET Content = (
	REPLACE (
		Content ,@oldlink1 ,@newlink1
	)
)
WHERE
	Content LIKE concat('%' ,@oldlink1, '%');

　

2.连表删除数据

SET @UnitId = '27542';

DELETE t1
FROM
	Test1 AS t1
INNER JOIN Test2 AS t2 ON t1.Code = t2.Code
WHERE
	t2.UnitId NOT IN (@UnitId);

　　

3.连表插入数据

INSERT INTO Test (
	ID,
	PostTime
) SELECT
	UUID() AS ID,
	t1.PostTime
FROM
	Test1 AS t1
INNER JOIN Test2 AS t2 ON t1.Code = t2.Code;

4. 连表更新数据

UPDATE Test1 AS t1
INNER JOIN Test2 AS t2 ON t1.Code = t2.Code
SET t1.NextFlowNodeId = 72
WHERE
	t1.ProcessStepId = 70;

5.获取某个库下的所有表名

select table_name from information_schema.tables where table_schema=@dbName

　　

6.获取某个表的所有字段名

select COLUMN_NAME from information_schema.COLUMNS where table_name = @tableName and table_schema = @dbName;

7.CONCAT 拼接字符串

SET @SearchText= CONCAT（'%'，'测试','%'）；
SELECT * FROM  Test3 WHERE CONCAT(ItemName,ItemNumber,DeptName,RealName) LIKE @SearchText；

 注意：若拼接项中存在NULL值，结果为NULL。如 CONCAT('测试','001',NULL,'小明'),结果为NULL，并不是我们想要的结果："测试001小明"

8.删除本表重复数据（You can’t specify target table for update in FROM clause，嵌套一层处理）

DELETE
FROM
    A
WHERE
    id IN (
        SELECT
            tt.*
        FROM
            (
                SELECT
                    t1.id
                FROM
                    A AS t1
                WHERE
                    objectid = 'S'
                AND Enabled = 0
                AND EXISTS (
                    SELECT
                        *
                    FROM
                        A AS t2
                    WHERE
                        objectid = 'S'
                    AND t1.UserId = t2.UserId
                    GROUP BY
                        UserId
                    HAVING
                        COUNT(id) >= 2
                )
            ) AS tt
    );