Question

Would it be possible to construct SQL to concatenate column values from
multiple rows?

The following is an example:

Table A

PID
A
B
C

Table B

PID   SEQ    Desc

A     1      Have
A     2      a nice
A     3      day.
B     1      Nice Work.
C     1      Yes
C     2      we can 
C     3      do 
C     4      this work!

Output of the SQL should be –

PID   Desc
A     Have a nice day.
B     Nice Work.
C     Yes we can do this work!

So basically the Desc column for out put table is a concatenation of the SEQ values from Table B?

Any help with the SQL?

Answer 1

There are a few ways depending on what version you have – see the oracle documentation on string aggregation techniques. A very common one is to use LISTAGG:

SELECT pid, LISTAGG(Desc, ' ') WITHIN GROUP (ORDER BY seq) AS description
FROM B GROUP BY pid;

Then join to A to pick out the pids you want.

Note: Out of the box, LISTAGG only works correctly with VARCHAR2 columns.