Php inquires if it has been inserted before it inserts or triggers the mysql unique constraint. What's going on?

I built a unique index. When inserting data, I first search in the database. The program is Synchronize. It queries, judges, and then inserts. There is only one database. I do not know why I look at the php_error log, or trigger the constraint of this unique index.

Mar.05,2021

if it is a website, it is still possible to be concurrent, because php will create different processes for different users.


indicates that someone has inserted it.

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