SQL’s Order Of Execution is From(Join), Where, Group by, Having, Select, Order by, Limit. Why can the Select's alias be used in the Having clause?

Hi Ramsey! Thanks for reaching out. The order MySQL executes the statements is the following: FROM clause WHERE clause SELECT clause GROUP BY clause HAVING clause ORDER BY clause This is important for understanding how queries are parsed. You cannot use a column alias defined in a SELECT in the WHERE clause, for instance, because the WHERE is parsed before the SELECT. On the other hand, such an alias can be in the GROUP BY, HAVING and ORDER BY clause. Hope this helps. Best, Tsvetelin

Your parsing order appears to be different from what I was taught. Do you have a source to back up your statement? I'm curious if the order of parsing differs between RDBMS.

Hi Ramsey and Tsvetelin! I hope you don't mind if I join the conversation. @Ramsey: Can you please share the order you are referring to? Which steps are the ones that seem incorrect/strange to you and which version of the SQL language (i.e. database) are you referring to? The order Tsvetelin has provided certainly refers to the way the Optimizer works in MySQL. Looking forward to your reply. Kind regards, Martin

Well, I was taught (example book: SQL Pocket Guide, 3rd Edition published by O'REILLY) , the order of execution in SQL is: FROM (and JOINs) clause WHERE clause GROUP BY clause HAVING clause SELECT (and DISTINCT) clause ORDER BY clause LIMIT clause I just don't get how a SELECT clause can be parsed before, for example, grouping the rows. Thank you Ramsey