Question

我有一个列，我想从最常值中按降序返回不同的值，而不是匹配某些条件。

该列包含以下记录：

this 
those
that
dog
these
here
there
cat
dog
hamster
hamster
there
blah
here
blah
blah
dog

所以我有：

SELECT DISTINCT(rcolumn)
FROM otable
WHERE reason != 'this'
AND reason != 'that'
AND reason != 'those'
AND reason != 'these'
AND reason != 'them'
AND reason != 'here'
AND reason != 'there'
AND reason != 'in between'
AND reason != 'all over'
AND reason != 'something'
AND reason != 'something else'
AND reason != 'anywhere'
AND reason != 'anywhere else'

将返回：

blah
cats
hamsters
dogs

但我希望它能回归：

blah
dogs
hamsters
cats

按顺序，因为blah出现在桌子上，然后是狗，然后是仓鼠，然后是猫。

Answer 1

为了按频率顺序返回内容，您需要GROUP BY值：

SELECT   rcolumn
FROM     otable
-- WHERE stuff
GROUP BY rcolumn;

这应该给出与你所拥有的答案基本相同的答案。然后，您可以轻松计算每行的发生率并进行排序：

SELECT   rcolumn, COUNT(*) AS frequency
FROM     otable
GROUP BY rcolumn
ORDER BY frequency DESC;

如果您不希望在结果中看到计算出的频率列，那么您可以直接订购：

SELECT   rcolumn
FROM     otable
GROUP BY rcolumn
ORDER BY COUNT(*) DESC;

通常，在使用GROUP BY子句时，请注意只选择：

您按
汇总功能的结果

大多数RDBMS会将此视为错误，但MySQL会选择一个随机行并返回该数据。

最后为了更加清晰，为什么不将长WHERE子句更改为更优雅的内容：

WHERE rcolumn NOT IN
    ('this'
    ,'that'
    ,'those'
    -- ...
)

Answer 2

只需在声明的末尾添加ORDER BY COUNT(rcolumn) DESC

即可

SELECT DISTINCT rcolumn
FROM otable
WHERE reason != 'this'
AND reason != 'that'
AND reason != 'those'
AND reason != 'these'
AND reason != 'them'
AND reason != 'here'
AND reason != 'there'
AND reason != 'in between'
AND reason != 'all over'
AND reason != 'something'
AND reason != 'something else'
AND reason != 'anywhere'
AND reason != 'anywhere else'
ORDER BY COUNT(rcolumn) DESC
;

选择频率顺序最常出现的值

2 个答案: