在mysql查询中限制结果

Question

I have two mysql tables called users and images. Every user have up to 5 pictures. In a page I show users information plus one image (first uploaded). When I do query like this

SELECT
  SQL_CALC_FOUND_ROWS,
  u.username,
  u.gender,
  u.etc
  .........
  i.picture
FROM users u
LEFT JOIN images i on u.id = i.id
WHERE 
 some_condition

and if the user has two uploaded images mysql result is 2 rows. If the images are 3 returned rows are 3 and so on. How to do so the result to be just one row (one pictue) ?

I tried to add LIMIT 0, 1 but SQL_CALC_FOUND_ROWS returns the actual number of pictures.

Answer 1

You could use a case when clause. I'm not a MySQL person, but you could try something like this:

SELECT
  case 
    when SQL_CALC_FOUND_ROWS > 5 then '5'
    else SQL_CALC_FOUND_ROWS
  end,
  u.username,
  u.gender,
  u.etc
  .........
  i.picture
FROM users u
LEFT JOIN images i on u.id = i.id
WHERE 
 some_condition

Answer 2

SQL_CALC_FOUND_ROWS will return the number of rows in the full result set, whereas a LIMIT statement tells the query to only return a limited number of rows from that result set.

I don't see why you need to use SQL_CALC_FOUND_ROWS at all here, you can just count the number of rows in the last result set (and use a LIMIT).

$count = mysql_num_rows($result)

Answer 3

你可以做

select max(i.uploadDate) group by (u.id)