MySQL查询-获取“大于…”的列值

Question

I have this query:

$score = 10;
SELECT timecode, count(tag) as n_tags, tag
FROM dados
WHERE dados.tag = 'tag1' 
AND dados.filename = 'file.mp4'
AND (timecode >= '-5' AND timecode <= '15')
AND (timecode = '$score')
GROUP BY timecode
ORDER BY count(tag) DESC

However I want to change the 6 line to:

AND (timecode = '$score' AND n_tags > 3)

but it doesn't seems the correct way to do, it doesn't work.

Any ideas ?

Answer 1

Remove that line from your WHERE clause and put in a HAVING clause. A HAVING clause will look at aggregate results. WHERE does not.

SELECT timecode, count(tag) as n_tags, tag
FROM dados
WHERE dados.tag = 'tag1' 
AND dados.filename = 'file.mp4'
AND (timecode >= '-5' AND timecode <= '15')
AND (timecode = '$score')
GROUP BY timecode
HAVING count(tag) > 3
ORDER BY count(tag) DESC

This line is redundant and could be dropped: AND (timecode >= '-5' AND timecode <= '15')

SELECT timecode, count(tag) as n_tags, tag
FROM dados
WHERE dados.tag = 'tag1' 
AND dados.filename = 'file.mp4'
AND (timecode = '$score')
GROUP BY timecode
HAVING count(tag) > 3
ORDER BY count(tag) DESC

Answer 2

You can't use aggregated fields in a WHERE clause. count() results are only available after ALL applicable rows have been considered. But the where filtering is done as each individual row is parsed. Cliche statement, but you're trying to count your chickens before they've hatched.

Such things have to be done with a HAVING clause, which is basically exactly the same as a where , but is applied just before the final results are sent back to the client. So...

SELECT ..., count(tag) as n_tags
...
WHERE (timecode = '$score')

HAVING (n_tags > 3)