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Editorial Team
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Asked: 2026-06-17T16:56:37+00:00

I’m trying to migrate some data from two tables into a new table and

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I’m trying to migrate some data from two tables into a new table and having a hard time figuring out how to do it.

Data: 

table fh rows: A, B, C, X, Y
table fhgb rows: B, C
table gvsi (currently empty) rows: A, X, Y
A is unique, and B+C is unique

When done, table gvsi should contains all rows in fh where X=value and the row isn’t already in fhgb.

This is a one-time data migration to gvsi so performance isn’t a huge deal.
fh has 36 million rows with 12 million that I care about (where X=value).
fhgb has 10 million rows. I’m expecting gvsi to contain about 2 million rows (12mil-10mil) when done.

I’ve googled and tried lots of things but can’t get anything to work (JOINs, subqueries, etc.) Can anyone help me figure out how to do this?

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1 Answer

  1. Editorial Team

    Our DB guy came up with the answer in 2 minutes:

    INSERT INTO gvsi (A, B, X, Y)
SELECT fh.A, fh.B, fh.X, fh.Y
FROM
f_h fh
LEFT OUTER JOIN f_h_g_b fhgb ON fh.A=fhgb.A and fh.B=fhgb.B
WHERE fhgb.A IS NULL

    That’s not to say some of these answers won’t work, but this one worked first try. Thanks for looking at it. I should try some of these other answers too and see if they work and if they work faster.

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