Question

请参阅此sqlfiddle.com/#!2/04c61/4（包含多列（十进制）的表格）。

我希望从该表中的所有单元格中获取最小值0零值。

我试过这个sql

SELECT
LEAST(
MIN(IF(sgl_ro=0,'NULL',sgl_ro))
,MIN(IF(sgl_bb=0,'NULL',sgl_bb))
,MIN(IF(sgl_hb=0,'NULL',sgl_hb))
,MIN(IF(sgl_fb=0,'NULL',sgl_fb))
) AS MinRate
FROM room_rates
WHERE hotel_id='1'
GROUP BY hotel_id;

但是它给了我错误的值（我想因为有多行。如果有一行，它会返回正确的值）。

感谢。

Answer 1

这是一个解决方案：

SELECT least(MIN(nullif(sgl_ro,0))
            ,MIN(nullif(sgl_bb,0))
            ,MIN(nullif(sgl_hb,0))
            ,MIN(nullif(sgl_fb,0)) ) as min_rate
FROM room_rates
WHERE hotel_id='1'
;

编辑：使用NULL而不是＆＃39; NULL＆＃39;

＆＃39; NULL＆＃39;是一个字符串，MySQL有关于如何在类型之间进行转换的非常奇怪的想法：

select case when 0 = 'NULL' 
            then 'ohoy' 
            else 'sailor' 
       end 
from room_rates;

ohoy
ohoy
ohoy

即。你解决方案将删除＆＃39;来自NULL：

SELECT
LEAST(
MIN(IF(sgl_ro=0,NULL,sgl_ro))
,MIN(IF(sgl_bb=0,NULL,sgl_bb))
,MIN(IF(sgl_hb=0,NULL,sgl_hb))
,MIN(IF(sgl_fb=0,NULL,sgl_fb))
) AS MinRate
FROM room_rates
WHERE hotel_id='1'
;

MINRATE
9

编辑：DBMS之间的比较：

我在sqlfiddle + DB2 10.5中测试了所有可用DBMS的以下场景：

create table t(x int);
insert into t(x) values (1);
select case when 0 = 'NULL' 
        then 'ohoy' 
        else 'sailor' 
   end 
from t;

所有mysql版本都返回了＆oh;＆＃39;

sql.js返回＆＃39; sailor＆＃39;

所有其他人（包括DB2 10.5）都认为该查询是非法的。

编辑：处理行中所有列（或列的所有行）= 0

的情况

select min(least(coalesce(nullif(sgl_ro,0), 2147483647)
                ,coalesce(nullif(sgl_bb,0), 2147483647)
                ,coalesce(nullif(sgl_hb,0), 2147483647) 
                ,coalesce(nullif(sgl_fb,0), 2147483647) ) )  
FROM room_rates
WHERE hotel_id='1'
  AND coalesce(nullif(sgl_ro,0), nullif(sgl_bb,0)
              ,nullif(sgl_hb,0), nullif(sgl_fb,0)) IS NOT NULL;

Answer 2

一步一步解决另一个问题：

从一列获取最小值：

SELECT MIN(sgl_ro) AS MinRate, hotel_id
   FROM room_rates
   WHERE sgl_ro != 0 AND hotel_id='1'
   GROUP BY hotel_id

从所有列中获取最小值并聚合到最小值（最终查询）：

SELECT MIN(MinRate) AS MinRate
FROM (
  SELECT MIN(sgl_ro) AS MinRate, hotel_id
     FROM room_rates
     WHERE sgl_ro != 0 AND hotel_id='1'
     GROUP BY hotel_id
  UNION 
  SELECT MIN(sgl_bb) AS MinRate, hotel_id
     FROM room_rates
     WHERE sgl_bb != 0 AND hotel_id='1'
     GROUP BY hotel_id
  UNION 
  SELECT MIN(sgl_hb) AS MinRate, hotel_id
     FROM room_rates
     WHERE sgl_hb != 0 AND hotel_id='1'
     GROUP BY hotel_id
  UNION 
  SELECT MIN(sgl_fb) AS MinRate, hotel_id
     FROM room_rates
     WHERE sgl_fb != 0 AND hotel_id='1'
     GROUP BY hotel_id
  ) res
GROUP BY hotel_id

测试它：http://sqlfiddle.com/#!2/3b156/1

MySQL：从所有列中获取表格的MIN值＆amp;行

2 个答案: