Question

I need to simulate the left join effect without using the “left join” key.

I have two tables, A and B, both with id and name columns. I would like to select all the dbids on both tables, where the name in A equals the name in B.

I use this to make a synchronization, so at the beginning B is empty (so I will have couples with id from A with a value and id from B is null). Later I will have a mix of couples with value – value and value – null.

Normally it would be:

SELECT A.id, B.id
FROM A left join B
ON A.name = B.name

The problem is that I can’t use the left join and wanted to know if/how it is possible to do the same thing.

Answer 1

you can use this approach, but you must be sure that the inner select only returns one row.

SELECT A.id, 
(select B.id from B where  A.name = B.name) as B_ID
FROM A