Question

I have one complicated question. I’ll try to explain it with example:

have one table that have primary key, and I want to join other table there the first’s table primary key is foreign key, and I want If in the second table there is duplicate foreign key to select the number of repeatability. For example:

1-st table:

  id    name 
  ---  -----
  1     Greg
  2     Alan 
  3    George 
  4     John 
  5     Peter   

2-nd table

 id       aid        data   
 ---     -----      -------
 1        2          CCCV   
 2        2          VVVV 
 3        3          DDDDD 
 4        3          SSSS 
 5        4          PPPPP 

I want the result of the join to be:

 id(1st table)  aid   name    Data   Number
 -----------    ----  -----   -----  -----
 1               null  Greg    null   1
 2                1    Alan    CCCV   1
 2                2    Alan    VVVV   2
 3                3    George  DDDDD  1
 3                4    George  SSSS   2
 4                5    John    PPPPP  1
 5               null  Peter   null   1

I searched a lot, I couldn’t find anything. Maybe I do not know how search, or there is no such thing as what I want to do.

Answer 1

SELECT Table1.id, Table2.id as aid, Table1.name, Table2.data,
GREATEST(1, (SELECT COUNT(*)
             FROM Table2 t2
             WHERE t2.aid = Table1.id
             AND t2.id <= Table2.id))
AS number
FROM Table1
LEFT JOIN Table2
ON Table2.aid = Table1.id
ORDER BY id, aid;

works in both MySQL and PostgreSQL.