mysql查询数据，根据条件更新到另一张表

原本的数据库有3张表

travel_way ：旅游线路表，存放线路的具体信息

traveltag ：线路标签表，存放线路目的地等信息

tagrelation：标签对应表，存放线路和目的地的对应关系

因为业务逻辑的改变，现在要把它们合并为一张表，把traveltag中的目的地信息插入到travel_way中。

首先获取到所有线路对应的目的地，以线路ID分组，合并目的地到一行，以逗号分隔。

SELECT travel_way.id,GROUP_CONCAT(traveltag.content) FROM travel_way LEFT JOIN tagrelation on travel_way.id = tagrelation.travel_id LEFT JOIN traveltag ON tagrelation.tag_id = traveltag.id GROUP BY travel_way.id

先把查到的数据存放到了一个新建的表mid里

INSERT into mid (travelway_id,destination) SELECT travel_way.id,GROUP_CONCAT(traveltag.content) FROM travel_way LEFT JOIN tagrelation on travel_way.id = tagrelation.travel_id LEFT JOIN traveltag ON tagrelation.tag_id = traveltag.id GROUP BY travel_way.id

然后将mid表的数据更新到travel_way里，因为是更新，所以不能用insert into select from 语句了

update travel_way,mid set travel_way.destination = mid.destination where travel_way.id = mid.travelway_id

成功将目的地以逗号分隔的字符串形式导入travel_way表中

说一下用到的几个方法，group_concat

group_concat( [DISTINCT] 要连接的字段 [Order BY 排序字段 ASC/DESC] [Separator ‘分隔符’] ),该函数能够将相同的行组合起来

select * from goods;

+------+------+
| id| price|
+------+------+
|1 | 10|
|1 | 20|
|1 | 20|
|2 | 20|
|3 | 200 |
|3 | 500 |
+------+------+
6 rows in set (0.00 sec)

以id分组，把price字段的值在同一行打印出来，逗号分隔(默认）

select id, group_concat(price) from goods group by id;
+------+--------------------+
| id| group_concat(price) |
+------+--------------------+
|1 | 10,20,20|
|2 | 20 |
|3 | 200,500|
+------+--------------------+
3 rows in set (0.00 sec)

以id分组，把price字段去重打印在一行，逗号分隔

select id,group_concat(distinct price) from goods group by id;
+------+-----------------------------+
| id| group_concat(distinct price) |
+------+-----------------------------+
|1 | 10,20|
|2 | 20 |
|3 | 200,500 |
+------+-----------------------------+
3 rows in set (0.00 sec)

以id分组，把price字段的值打印在一行，逗号分隔，按照price倒序排列

select id,group_concat(price order by price desc) from goods group by id;
+------+---------------------------------------+
| id| group_concat(price order by price desc) |
+------+---------------------------------------+
|1 | 20,20,10 |
|2 | 20|
|3 | 500,200|
+------+---------------------------------------+
3 rows in set (0.00 sec)

insert into select from 将查询到的记录插入到某个表中，

INSERT INTO db1_name(field1,field2) SELECT field1,field2 FROM db2_name

要求目标db2必须存在，下面测试一下，有两个表，结构如下

select * from insert_one;
+----+--------+-----+-----+
| id | name   | age | sex |
+----+--------+-----+-----+
|  1 | 田小斯 | 25  |     |
|  2 | 刘大牛 | 26  |     |
|  3 | 郑大锤 | 28  |     |
|  4 | 胡二狗 | 30  |     |
+----+--------+-----+-----+
4 rows in set

select * from insert_sex;
+----+-----+
| id | sex |
+----+-----+
|  1 | 1   |
|  2 | 2   |
|  3 | 1   |
|  4 | 2   |
+----+-----+
4 rows in set

从表2中查找性别数据，插入到表1中

into insert_one(sex) select sex from insert_sex;
Query OK, 4 rows affected
select * from insert_one;
+----+--------+-----+-----+
| id | name   | age | sex |
+----+--------+-----+-----+
|  1 | 田小斯 | 25  |     |
|  2 | 刘大牛 | 26  |     |
|  3 | 郑大锤 | 28  |     |
|  4 | 胡二狗 | 30  |     |
|  5 |        |     | 1   |
|  6 |        |     | 2   |
|  7 |        |     | 1   |
|  8 |        |     | 2   |
+----+--------+-----+-----+
8 rows in set

结果很尴尬，我是想要更新这张表的sex字段，而不是插入新的数据，那么这个命令只适用于要把数据导入空表中，所以在上面的实际需要中，我建立了新表mid，利用update来中转并更新数据

UPDATE tb1,tb2 SET tb1.address=tb2.address WHERE tb1.name=tb2.name

根据条件匹配，把表1的数据替换为（更新为）表2的数据，表1和表2必须有关联才可以

update insert_one,insert_sex set insert_one.sex = insert_sex.sex where insert_one.id = insert_sex.id;
Query OK, 4 rows affected
select * from insert_one;
+----+--------+-----+-----+
| id | name   | age | sex |
+----+--------+-----+-----+
|  1 | 田小斯 | 25  | 1   |
|  2 | 刘大牛 | 26  | 2   |
|  3 | 郑大锤 | 28  | 1   |
|  4 | 胡二狗 | 30  | 2   |
|  5 |        |     | 1   |
|  6 |        |     | 2   |
|  7 |        |     | 1   |
|  8 |        |     | 2   |
+----+--------+-----+-----+
8 rows in set

成功将数据更新到insert_one表的sex字段中。