Check before INSERT INTO - Mailing list pgsql-sql

From Shavonne Marietta Wijesinghe
Subject Check before INSERT INTO
Date
Msg-id 010901c86ca6$3b66e870$3102a8c0@dream
Whole thread Raw
Responses Re: Check before INSERT INTO
List pgsql-sql
My table structure
 
CREATE TABLE my_shevi
(
  id text,
  n_gen serial NOT NULL,
  n_sheet serial NOT NULL,
  tot_sheet serial NOT NULL,
  CONSTRAINT my_shevi_pkey PRIMARY KEY (n_gen, n_sheet, tot_sheet)
)
WITH OIDS;
ALTER TABLE my_shevi OWNER TO postgres;
 
The user updates the DB via ASP. When 2 users click on the submit button at the same time, only 1 record is inserted. (ERROR:  duplicate key violates unique constraint "my_shevi_pkey")
 
For example they both send a string like below.
strSQL = INSERT INTO my_shevi VALUES ('a', 4, 1, 1);
 
I thought of adding a test before executing the insert into. 
 
Set SQLN_GEN = oConn.Execute("SELECT upper(N_GEN), upper(N_SHEET), upper(TOT_N_SHEET) FROM " & TableName & " WHERE N_GEN='" & n_gen & "' AND N_SHEET='" & n_sheet & "' AND TOT_N_SHEET='" & tot_n_sheet & "'")
 
if (not SQLN_GEN.eof) then
     ***** set n_gen + 1  
else
     ***** leave n_gen the way it is
end if
 
conn.Execute strSQL

But how can i ask it to change the n_gen value??? (The part with the *****)
 
Thanks
 
Shavonne Wijesinghe

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