I have what seems like a pretty simple problem. I want to combine table A with table B to get table C 

table A

tok count
a   1
b   1

table B

tok count
b   1
c   1

table C (desired)

tok count
a   1
b   2
c   1

[download]
Constraints.
  1. The end goal is speed
  2. I have to use MySQL
  3. I have 2GB of RAM but the tables are so big (multiple millions of rows) reading into a Perl hash and incrementing count there is not an option. We do this already with 'small' < 2GB sets of data as it drop the runtime from hours to minutes
  4. tok is a primary key

What I want to do is encapsulated in this pseudocode 

INSERT INTO all_tok (tok, tok1.count+tok2.count) 
SELECT tok, count from tok1
UNION
SELECT tok, count from tok2

[download]

I need a union not a join as the final table needa to contain all the toks (at least that is what I think). If a tok exists in one table but not the other I just want the count from the table it exists in. If it does exist in both tables I need the sum of the counts. I have beaten my head against the proverbial wall for some hours. It didn't help, the only good thing was it felt good when I stopped ;-).

Any suggestions about approaches to this seemingly simple task gratefully received. Temp tables are fine.

cheers

tachyon

In reply to OT: MySQL combine 2 tables data when Perl 'fails' by tachyon

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