🤹‍♀️ SELECT ORDER [SQL]

• Why can't use SUM() in WHERE?
• Why can't use AS in WHERE or GROUP BY?

😎 You will get the reason why it is like that

💎 Select order

When you see this SQL, what do you think about order?

SELECT * FROM clients WHERE age >= 30 GROUP BY usa HAVING salary > 1000 ORDER BY id desc LIMIT 100 

Seems like sql executes from SELECT ?
actually it's not true

-- SQL executes in this order FROM | WHERE | GROUP BY | HAVING | SELECT | ORDER BY | LIMIT 

💎 Question 1

Why SUM() function can't use in WHERE?

FROM | WHERE 👈 👈 | GROUP BY 👈 👈 | HAVING | SELECT | ORDER BY | LIMIT 

Before WHERE executes, GROUP BY has not executed yet, so we can't use COUNT() SUM() in WHERE.

In other word, it's possible to use these functions in HAVING.

💎 Question 2

Why can't use AS in WHERE or GROUP BY? Even though in ORDER BY can use it, unfair!!

FROM | WHERE 👈 👈 | GROUP BY 👈 👈 | HAVING | SELECT 👈 👈 | ORDER BY 👀 👀 | LIMIT 

take it easy, man. Because ORDER BY executes after SELECT.
You can't read name which is created by "AS" before define it.

Thank you for reading 🤗