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Hi Masters,

I am looking for a better approach for the below requirement with out using Union

Input table:  (total volume will be 100 million records)

Col1

Col2

Col3

1

1

1

1

2

2

1

2

I'm relatively new to database development in general and I've got a question related to the use of CASE statements when joining tables. Here's the situation I'm faced with.

I have a table (T1) that looks like this:
key1 key2 key3 key4
aaa zz 1 2
aaa zz 2 3
bbb yy 2 3
ccc xx 3 4

And another table (T2) that looks like this:
key1 key2 key3 key4
aaa zz 1 2
bbb yy ^ ^
ccc xx 3 ^

As you can see the keys in T2 are not always the same as T1 (don't ask why). But I need to use as many of the keys as I can in the join. What I coded is this:
ON
T1.key1 = T2.key1