MySQL execution order

Hello everyone , I meet you again , I'm your friend, Quan Jun .

mysql The order of execution is as follows ：

1. from Stage

2. where Stage

3. group by Stage

4. having Stage

5. select Stage

6. order by Stage

7. limit Stage

problem ： Why can't aliases be used in where in , But it can be used in order by in ？

according to mysql Execution order of , You can know , The above code executes from score , I'll do it again where , Finally implemented select . Aliases are generated in the fifth query phase , With the alias , Can only be used in later execution stages , in other words , Aliases can only be used for queries after phase 5 . therefore where total >= 200 Execution time , Alias has not been generated total, So compilation error .

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