Hi,
I have a table that has many rows. I want to be
able to insert a new row only if has a unique field of
the last 20 rows when I sort them by date.
Currently before I insert a new row, I will select a
specific field for 20 rows and run a for loop in php
looking for a match with the data I'm getting ready to
insert. If a match occurs I will skip the insert
command.
This normally works fine, but I have seen occasions
when 2 people visit my website at the same exact time.
In this case, sometimes I might insert the data twice
because I think I'm spinning in the for loop for 2
site visitors simultaneously.
I know this is bad syntax, but this is what I imagine
a insert query to look like:
INSERT INTO $table (datax, datay, dataz)
VALUES ('x', 'y', 'z') IF 'x' unique WHEN
ordering by 'z' DESC LIMIT 20
In this example, 'z' is a datetime field and 'x' is a
varchar. I don't mind duplicate entries in my table,
but I don't want duplicates entries to occur within 20
rows when sorting by date.
Is this possible to do with one INSERT command? I saw
the IGNORE statment in the mysql manual, but I don't
think it really aplies to what I'm trying to do here.
Any suggestions would be appreciated,
Thanks,
Grant
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