Tracking differences between two SQL tables (added, removed, changed)

Question

Suppose I have the following table A :

create table A (
    code-id integer primary key,
    code-name-1 varchar(200) not null,
    code-name-2 varchar(200) not null,
    foreign key (code-id) references another-table(code-id)
);

And one more table, B :

create table B (
    code-id integer primary key,
    code-name-1 varchar(200) not null,
    code-name-2 varchar(200) not null,
    foreign key (code-id) references another-table(code-id)
);

Both tables, A and B hold unique code-id references into another-table which is not relevant to the question.

Is it possible to write a single query that can identify in one fell swoop:

• Which code-id s are in A but not in B .
• Which code-id s are in B but not in A .
• Which code-id s are the same in A and B , but their code-name-1 or code-name-2 values are different (either of them).

I believe that this could be solved by one left join clause, with its results concatenated to a right join clause, with its results concatenated to a third inner join clause, enhanced with two string comparison predicates for the on clause.

• Am I on the right track?

• Can I generate an additional column specifying the result of the operation? Eg column RESULT with values ADDED , REMOVED , CHANGED ?

• Is there a more clever way to specify this query, rather than having to concatenate three join clauses?

Thanks!

Answer 1

In A but not in B

Select code-id from A
Except
Select code-id from B

In B but not in A

Select code-id from B
Except
Select code-id from A

In Both A and B

Select code-id from A
Intersect
Select code-id from B

As a single query, you should be able to UNION them Together

Select code-id from A
    Except
    Select code-id from B
UNION
Select code-id from B
    Except
    Select code-id from A
UNION
Select code-id from A
    Intersect
    Select code-id from B

Answer 2

You may use EXCEPT operand and one join like this

Select code-id, 'added' result from a
Except
Select code-id, 'added' result from b
Union all
Select code-id, 'removed' result from b
Except
Select code-id, 'removed' result from a
Union all
Select code-id, 'changed' result 
from a join b on a.code-id = b.code-id 
Where a.code-name-1 != b.code-name-1 or a.code-name-2 != b.code-name-2