Question

我已经写了左连接查询，我希望左表的product_code列应该由右表的product_code列按以下查询条件更新

update stock_details_mt as s  left join 
(select min(product_code),product_name,mrp,sales_rate from stock_details_mt  group by product_name,mrp,sales_rate having count(*)>1)as s2  set
 s.product_code=s2.product_code on s.product_name=s2.product_name where s.mrp=s2.mrp and s.sales_rate=s2.sales_rate ;

Answer 1

你似乎已经失去了连接和集之间的情节，我会怀疑左连接。试试这个。

update stock_details_mt as s join 
(select min(product_code) product_code,product_name,mrp,sales_rate 
from stock_details_mt  
group by product_name,mrp,sales_rate 
having count(*)>1) as s2  
on s.product_name=s2.product_name and s.mrp=s2.mrp and s.sales_rate=s2.sales_rate 
set  s.product_code=s2.product_code 
where  1 = 1;

所以给出

drop table if exists stock_details_mt;

create table stock_details_mt
(product_code int, product_name varchar(10), mrp int, sales_rate int);

insert into stock_details_mt values
(2,'aaa',1,1),(1,'aaa',1,1),(10,'aaa',1,1),
(10,'bbb',1,1);

结果

+--------------+--------------+------+------------+
| product_code | product_name | mrp  | sales_rate |
+--------------+--------------+------+------------+
|            1 | aaa          |    1 |          1 |
|            1 | aaa          |    1 |          1 |
|            1 | aaa          |    1 |          1 |
|           10 | bbb          |    1 |          1 |
+--------------+--------------+------+------------+
4 rows in set (0.00 sec)

如何为左连接编写查询

1 个答案: