sathish kumar shanmugavelu wrote:
INSERT INTO rcp_patient_visit_monitor (
entry_no, patient_id, visit_date, is_newpatient,
visit_type, is_medical,
is_review, is_labtest, is_scan, is_scopy, is_xray,
weight, height)
VALUES ((SELECT coalesce(max(entry_no)+1, 1) FROM
rcp_patient_visit_monitor),?,current_timestamp,?,?,?,?,?,?,?,?,?,?)
The point to note here is the select statement which gets the max
entry_no and adds one to it and save the new value. entry_no is the primary
key of the above table.
Now i run the same program (different instance) from two systems, save
the form simultaneously, only one entry is saved, in the other system the
error says - duplicate key violates.
BEGIN;
LOCK TABLE ...
INSERT ...
COMMIT;
You'll need to handle possible errors where one client fails to get a
lock and times out. It won't happen often, but you do need to consider
the option.
--
Richard Huxton
Archonet Ltd
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