Postgres User wrote:
I'm using this code to increment a counter table:
IF Exists (SELECT keyfld FROM counter_tbl WHERE key_fld = 'key_val') THEN
UPDATE counter_tbl SET counter_fld = counter_fld + 1
WHERE key_fld = 'key_val';
ELSE
INSERT INTO counter_tbl(key_fld, counter_fld) VALUES('key_val', 1);
END IF;
Now, I assume that it's possible for another session to INSERT a row
in the microseconds that exist between the Select and Insert
statements above.
I also assume that I can wrap the above code in a transaction, and if
the transaction fails (because another session's Insert causes my
Insert to fail), then I simply need to re-execute it once. (Updates
should never fail.)
Does anyone have a simple example of the best way to code this type of
transaction- and the best way to re-execute the same code on failure?
I could use a loop but I'm not sure if that's the best solution.
I think I would try the INSERT first. If it fails, then trap the
exception and do the UPDATE
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