多条语句中的mysql select语句
多条语句中的mysql select语句
提问于 2014-09-18 20:24:28
SET @row_number:=0;
SET @db_names:='';
SELECT @row_number:=CASE WHEN @db_names=app_id THEN @row_number+1 ELSE 1 END AS row_number,@db_names:=app_id AS db_names
FROM master_order
ORDER BY app_id ;当我运行这条语句时，它会给出结果。
我想要的是
select *from (SET @row_number:=0;
SET @db_names:='';
SELECT @row_number:=CASE WHEN @db_names=app_id THEN @row_number+1 ELSE 1 END AS row_number,@db_names:=app_id AS db_names
FROM master_order
ORDER BY app_id ) as temp
where row_number = 1;我想选择重复列的第一行
回答 1
Stack Overflow用户
发布于 2014-09-18 20:35:50
您可以将其简化为：
SELECT * FROM master_order
ORDER BY app_id = '' DESC, app_id
LIMIT 1;但是为了澄清它是如何工作的，如果这种简化是不可能的，不管是哪种方式：
SET @row_number:=0;
SET @db_names:='';
select *from (
SELECT @row_number:=CASE WHEN @db_names=app_id THEN @row_number+1 ELSE 1 END AS row_number,@db_names:=app_id AS db_names
FROM master_order
ORDER BY app_id
) as temp
where row_number = 1;或者这样：
select *from (
SELECT @row_number:=CASE WHEN @db_names=app_id THEN @row_number+1 ELSE 1 END AS row_number,@db_names:=app_id AS db_names
FROM master_order
CROSS JOIN (SELECT @row_number := 0, @db_names := '') var_init
ORDER BY app_id
) as temp
where row_number = 1;页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/25912548
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