id      admission       amount          paid_date

12      0001            1750            2012-09-23
13      0002            1750            2012-09-23
14      0010            1750            2012-09-23

SELECT *, (SELECT SUM(amount) )
FROM gains
WHERE  `paid_date`  LIKE '%2012-09-23%'
ORDER BY `paid_date`

id      admission       amount          paid_date     (SELECT SUM(amount) )

12      0001            1750            2012-09-23          5250

SELECT *,
      (SELECT SUM(amount)
       FROM gains
       WHERE  `paid_date` LIKE '%2012-09-23%') as sum_amount
FROM gains
WHERE  `paid_date`  LIKE '%2012-09-23%'
group by admission
ORDER BY `paid_date`

SELECT *, (SELECT SUM(amount) )
FROM gains
WHERE  `paid_date`  LIKE '%2012-09-23%'
GROUP BY admission