Issue with SQL inner join

Question

Ok so I have two mysql tables, the first one is " tbl_forum ":

|MSG_ID|MSG_QUERYID|MSG_ISPARENT| MSG_PARENTID
 1     | 59        | 1          | 1
 2     | 59        | 0          | 1

The second one is " tbl_frs ":

|FRS_ID|FRS_QUERYID|FRS_PARENTID | FRS_CONTENT
 1     | 59        | 1           | xxxx
 2     | 59        | 1           | yyyy

I want a query which would yield all rows of both tbl_forum and tbl_frs (join) where msg_queryid = 59 and msg_isparent = 1 . So in the example above I would like to get a single row which would look like this:

|MSG_ID|MSG_QUERYID|MSG_ISPARENT| MSG_PARENTID | FRS_ID|FRS_QUERYID|FRS_PARENTID | FRS_CONTENT
|1     |59         | 1          | 1            | 1     | 59        | 1           | xxxx

I tried this:

SELECT * from tbl_frs 
JOIN tbl_forum 
  ON msg_queryid=frs_queryid 
WHERE msg_isparent=1 

but it yielded two rows... (both msg_id 1 and 2...). How can I fix this?

edit

and the winner is:

 SELECT /column names.../ FROM tbl_frs JOIN tbl_forum ON tbl_frs.FRS_PARENTID=tbl_forum.MSG_ID WHERE tbl_frs.FRS_QUERYID=59 AND tbl_forum.MSG_ISPARENT=1

Answer 1

If I understand, you want to select ALL from your two tables where msg_queryid=frs_queryid AND msg_isparent=1 , right? Btw, using * is not a good practise, you should name your field !

Try this maybe:

SELECT 
    FRS.FRS_ID, FRS.FRS_QUERYID, FRS.FRS_PARENTID, FRS.FRS_CONTENT
    F.MSG_ID, F.MSG_QUERYID, F.MSG_ISPARENT, F.MSG_PARENTID
FROM tbl_frs as FRS
INNER JOIN tbl_forum as F ON F.MSG_QUERYID=FRS.FRS_QUERYID AND F.MSG_ISPARENT=1 

Answer 2

You should set the condition with FRS_ID=1 AND MSG_ISPARENT =1 then you will get your expect.

You can try this.

 SELECT 
    T1.MSG_ID,
    T1.MSG_QUERYID,
    T1.MSG_ISPARENT,
    T1.MSG_PARENTID,
    T2.FRS_ID,
    T2.FRS_QUERYID,
    T2.FRS_PARENTID,
    T2.FRS_CONTENT
FROM tbl_frs AS T2 
JOIN tbl_forum AS T1 ON T1.msg_queryid=T2.frs_queryid 
WHERE T2.FRS_ID=1  AND T1.MSG_ISPARENT =1

SQLFiddle

Answer 3

Please try below query:

SELECT * from tbl_forum JOIN tbl_frs ON msg_queryid = frs_queryid WHERE msg_isparent = 1

Thanks!

Answer 4

The query you have mentioned in your question has provided the correct answer to your problem.

SELECT * FROM tbl_frs JOIN tbl_forum ON msg_queryid = frs_queryid WHERE msg_isparent = 1

In the above query, you have told MySQL to fetch all rows where MSG_ISPARENT equals to 1 . So SQL takes the value from the column MSG_QUERYID (which is 59 ) and then it matches the value with tbl_frs.FRS_QUERYID .

Now there are two rows in FRS_QUERYID with value 59 . So MySQL will return two rows.

If you add the condition FRS_ID = 1 it won't meet your requirement. Be careful!!!

Because it won't return "all rows of both tbl_forum and tbl_frs (join) where msg_queryid = 59 and msg_isparent = 1 " .

The above query gives you the correct results. Don't change it unless you completely understand what's going on.