如何从每个列出现的SQL中获取值？

Question

I have a table called comments with the columns: posID and commentLikes .

   tableComments

|  postID   | commentLikes |
+-----------+--------------+
|  233      |      2       |
|  233      |      0       |
|  675      |      2       |
|  345      |      12      |
|  345      |      8       |

In my PHP code, I am passing the PostID variable to my function.
I want to get the number of likes for each post based on postID passed into the function so I will need the WHERE clause.

I have tried using COUNT and GROUP BY but still no luck. So I need to count each time the postID matches a value and then add up the total number of likes. How can I do this?

Answer 1

If you're passing a single postID you don't need a group by clause, you just need to use it in the where clause and sum the likes:

SELECT SUM(likes)
FROM   tableComments
WHERE  postId = ?

The "?" should of course be bound from the PHP code.

Answer 2

You don't need a GROUP BY since you will filter the records passed on the POstId you are passing.Just do a summation on the records you will get the desired results.

SELECT SUM(commentLikes)
FROM comments 
WHERE postID=@PostID