huanzi-qch

  前言

  最近需要写联表多字段update更新语句,发现不同的数据库,SQL语法也不一样,正好我这里有MySQL、Oracle、PgSQL三种数据库环境,分别练习、实操这三种数据库的联表update语句

  本文记录MySQL、Oracle、PgSQL联表多字段update更新语句实操练习过程

 

  练习需求

  一张user用户表、一张blog博客表,由于不同的数据库,sql语法不用,这里给出mysql的表数据语句,其他数据库类型自行转换

-- user用户表
CREATE TABLE `user`  (
  `user_id` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '用户id',
  `user_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '用户名称',
  PRIMARY KEY (`user_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '用户表' ROW_FORMAT = Compact;

INSERT INTO `user` VALUES ('1', '张三');
INSERT INTO `user` VALUES ('2', '李四');
INSERT INTO `user` VALUES ('3', '王五');
-- blog博客表
CREATE TABLE `blog`  (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '博客id',
  `title` varchar(200) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '博客标题',
  `content` mediumtext CHARACTER SET utf8 COLLATE utf8_general_ci NULL COMMENT '博客内容',
  `user_id` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '用户id',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 17 CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '博客表' ROW_FORMAT = Compact;

INSERT INTO `blog` VALUES (2, 'test 1', 'test 1', '1');
INSERT INTO `blog` VALUES (3, 'test 2', 'test 2', '1');
INSERT INTO `blog` VALUES (4, 'test 4', 'test 4', '2');
INSERT INTO `blog` VALUES (5, 'test 5', 'test 5', '2');
INSERT INTO `blog` VALUES (6, 'test 6', 'test 6', '1');
INSERT INTO `blog` VALUES (11, '11', '11', '3');
INSERT INTO `blog` VALUES (12, '12', '12', '3');
INSERT INTO `blog` VALUES (13, '13', '13', '3');
INSERT INTO `blog` VALUES (14, '14', '14', '3');
INSERT INTO `blog` VALUES (15, '15', '15', '3');
INSERT INTO `blog` VALUES (16, '16', '16', '3');

  练习需求:更新每个用户的博客id最大的博客内容,新内容为:用户名称user_name + 博客内容content

 

  需要修改的id,以及新内容

 

 

 

 

 

  SQL

  mysql

select * from blog
select * from `user`

-- 查出虚表table1
-- 练习需求:更新每个用户的博客id最大的博客内容,新内容为:用户名称user_name + 博客内容content
SELECT
    t.id,
    concat( t.user_name, b.content ) content 
FROM
    blog b
    JOIN (
    SELECT
        u.user_id,
        u.user_name,
        max( b.id ) AS id 
    FROM
        blog b
        JOIN `user` u ON u.user_id = b.user_id 
    GROUP BY
        u.user_id,
        u.user_name 
    ) t ON b.id = t.id

-- MySQL联表多字段update更新语句
update blog b ,(table1) t set b.content = t.content where b.id = t.id

  为了方便阅读避免贴出一堆长长的sql,此时update语句并不完整,执行时需要将table1虚表的查询sql,替换到下面的update语句中table1,再执行update语句

 

  oracle

select * from "blog"
select * from "user"

-- 查出虚表table1
-- 练习需求:更新每个用户的博客id最大的博客内容,新内容为:用户名称user_name + 博客内容content
SELECT
    t."id",
    concat( t."user_name", b."content" ) AS "content" 
FROM
    "blog" b
    JOIN (
    SELECT
        u."user_id",
        u."user_name",
        max( b."id" ) AS "id" 
    FROM
        "blog" b
        JOIN "user" u ON u."user_id" = b."user_id" 
    GROUP BY
        u."user_id",
        u."user_name" 
    ) t ON b."id" = t."id"

-- Oracle联表多字段update更新语句
update "blog" b set (b."content") = (select t."content" from (table1) t where b."id" = t."id")
where exists (select 1 from (table1) t where b."id" = t."id")

  为了方便阅读避免贴出一堆长长的sql,此时update语句并不完整,执行时需要将table1虚表的查询sql,替换到下面的update语句中table1,再执行update语句

 

  pgsql

select * from "blog"
select * from "user"

-- 查出虚表table1
-- 练习需求:更新每个用户的博客id最大的博客内容,新内容为:用户名称user_name + 博客内容content
SELECT
    t."id",
    concat( t."user_name", b."content" ) AS "content" 
FROM
    "blog" b
    JOIN (
    SELECT
        u."user_id",
        u."user_name",
        max( b."id" ) AS "id" 
    FROM
        "blog" b
        JOIN "user" u ON u."user_id" = b."user_id" 
    GROUP BY
        u."user_id",
        u."user_name" 
    ) t ON b."id" = t."id"
    
-- PgSQL联表多字段update更新语句
update "blog" b set b."content" = t."content" from (table1) t where b."id" = t."id"

  为了方便阅读避免贴出一堆长长的sql,此时update语句并不完整,执行时需要将table1虚表的查询sql,替换到下面的update语句中table1,再执行update语句

 

  练习效果

  以上三种数据库类型,SQL执行结果均为

 

 

 

  上大招

   实在不行了,可以直接拼接出update语句,再把update语句复制出来执行!

 

  我们以mysql为例(PS:由于单引号',是特殊字符,拼接时我们用$代替,后面再进行全部替换即可)

-- 查看、对比新旧数据
SELECT 
    t.id,
    b.content,
    concat( t.user_name, b.content ) new_content

-- 备份原数据
SELECT
    concat(
        concat( 'update blog set content = $', b.content ),
        concat( '$ where id = $', concat( t.id, '$;' ))
    ) AS str

-- update语句
SELECT
    concat(
        concat( 'update blog set content = $', concat( t.user_name, b.content ) ),
        concat( '$ where id = $', concat( t.id, '$;' ))
    ) AS str
    
FROM
    blog b
    JOIN (
    SELECT
        u.user_id,
        u.user_name,
        max( b.id ) AS id 
    FROM
        blog b
        JOIN `user` u ON u.user_id = b.user_id 
    GROUP BY
        u.user_id,
        u.user_name 
    ) t ON b.id = t.id

  查看、对比新旧数据

 

  备份原数据

 

 

 

 

  update语句

 

 

  这时候就可以愉快的执行update语句了 

 

  后记

  PS:执行update语句一定要带上where条件,否则一不小心就变成更新全表

  联表多字段update更新语句暂时先记录到这,后续再进行补充

分类:

sql

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