You can use the elimination method. The first step is to check whether the form can be submitted normally, and whether the parameters passed by the form can be obtained normally when processing the file. The second step is to check whether the database connection is available. The third step is to check whether the SQL statement is correct. OK First output the sql statement on the page, and then put the SQL statement into the database for execution. The fourth step is to check whether the conditions for successful execution are correct