联表多字段update更新语句

　　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