Mysql doubles the data in the database

In projects, you sometimes need to test the database performance or to test the paging effect. If one piece of data is inserted, the efficiency is obviously very low. The SQL statements added in batch are:

Insert tableName (name, password) select name, password from tablename

Some are called table migration. The test is as follows:

If the primary key of the table is auto-incrementing, replace the asterisk in the figure with the field name except the primary key (such as insert t1 (column1, column2) select (column1, column2) from t1 ).