Question

I want to compare fields in 2 tables to see if the fields have the same values.

For e.g.

– I have 2 tables, ‘products’ and ‘wishlist’.

– In both tables, they have the same fields ‘prodId’ and ‘userId’, plus other fields like ‘title’, etc.

– The ‘wishlist’ table contains some of the same rows that are in table ‘products’
(e.g. 10 in total in ‘products’ but only 6 of the same rows are in table ‘wishlist’)


– I want to display the fields/rows from table ‘products’, that are different from table ‘wishlist’, so from the e.g. it will only show 4 (so it does not show duplicates of the 6),
so to do this I would like to use fields ‘prodId’ and ‘userId’, in the table ‘products’, and compare this to the same fields in the table ‘wishlist’.

How would I do this?

Thanks.

Answer 1

A JOIN will return you all records that have matching values in both tables:

SELECT *
FROM
    products p
    JOIN wishlist w ON w.userId = p.userId AND w.prodId = p.prodId

---

EDIT:

To return all records that are not matching:

SELECT *
FROM
    products p
    FULL OUTER JOIN wishlist w ON w.userId = p.userId AND w.prodId = p.prodId
WHERE
    p.Id IS NULL
    OR w.Id IS NULL

---

EDIT:

To show records in products that don’t have a match in wishlist, use a LEFT JOIN:

SELECT *
FROM
    products p
    LEFT JOIN wishlist w ON w.userId = p.userId AND w.prodId = p.prodId
WHERE
    w.Id IS NULL