Question

I have SQL update query problem. I would like to be able to update one table using the results of a query against another table. Here is a simple example to show what I would like to do.

I have two tables:

TABLE1                      

ID     COUNT                                 
1       0         
2       0
3       0

Table2

ID
1
1
1
2


select id,count(*) from table2 group by id;

ID    COUNT
1       3
2       1

I can update one row at a time using this syntax:

update table1 set count=(select count(*) from table2 where id=1 group by id) where id=1;

What I would like is to be able to update all rows with one single sql statement so that the result would be:

TABLE1                      

ID     COUNT                                 
1       3         
2       1
3       0

Any ideas?

Answer 1

I think this might work for you:

update table1 
set count=
   (select count(*) 
    from table2 
    where table2.id=table1.id)