In MySQL, what is unique check disabled? What are the differences between uniqueness check, uniqueness constraints, and uniqueness indexes?

In MySQL, the uniqueness of the inserted data is checked. This uniqueness test also reduces the speed of data insertion. To optimize the insert record speed, you can disable the uniqueness check before inserting data and enable it after inserting data... I did the following two Tests. Why cannot I insert the same data after the uniqueness check is disabled ???? Test 1: first create a uniqueness constraint, and then disable the uniqueness check ():! IMG (img.ask.csdn.netupload201603071457317824_868341.png) test 2. create a unique index first, and then disable the uniqueness check (for example,... uniqueness check uniqueness constraint condition mysql uniqueness index optimization insert speed)

In MySQL, the uniqueness of the inserted data is checked. This uniqueness test also reduces the speed of data insertion. To optimize the insert record speed, you can disable the uniqueness check before inserting data and enable it after inserting data... I did the following two Tests. Why cannot I insert the same data after the uniqueness check is disabled ????
Test 1: first create a uniqueness constraint, and then disable the uniqueness check ():
Test 2: first create a unique index, and then disable the uniqueness check ():
In both tests, I disabled the uniqueness check. why cannot I insert the same id value? Please explain. thank you for being late ....