Question

I am new to mysql. I have a problem in inserting record to table1 if it does not exist in table2.I have 2 tables table1 and table2 in the form:

table1

dep_id  start     stop     modified deleted                 
1       23456789  167921525   Yes      No
2       34567812  345678145   Yes      No
3       32789054  327890546   No       No


table2

start     stop     modified deleted                 
23456789  167921525  No       No
34567823  345678145  No       No
32789053  727890546  No       No

I am trying to insert values into table1’s start and stop field values only if it does not exist in table2’s “start” and “stop” columns. If it exists the I need to throw an error.
These tables do not have a primary key foreign key relationship.
I apologize for not knowing correct syntax but I have to do something like this in mysql and PHP.

Replace Into into table1 set 'start'=> $start,'stop' => $stop
(select 'start','stop' from table2 where table1.start and table1.stop not in table2.start and table2.stop);

How do I query these 2 tables to check if Table1.start and Table1.stop fields do not match with Table2.start and Table2.stop before inserting to table1?

Answer 1

You can do:

INSERT INTO table1 (start, stop)
SELECT    a.*
FROM      (SELECT 123456789 start, 234567890 stop) a
LEFT JOIN table2 b ON (a.start,a.stop) IN ((b.start,b.stop))
WHERE     b.start IS NULL

Where 123456789 and 234567890 are your input values for start and stop respectively.

Then you can check it with rowCount or num_rows_affected based on what DB interface you’re using (PDO, mysqli, etc.). If it’s 0, then no record was inserted, otherwise, the insert occurred.

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SQLFiddle Demo