ALIAS cannot be used within WHERE clause

ALIAS cannot be used within WHERE clause. It produces an error like this. Just remember it, because it 100% guaranteed situation on your exam.

Even, if you remove double quotes from your ALIAS, the result still the same – it won’t work.

An alias can be used in a query select list to give a column a different name. You can use the alias in ORDER BY clause to refer to the column.

Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined.

Oracle Query Processing Order

  • FROM clause
  • WHERE clause
  • GROUP BY clause
  • HAVING clause
  • SELECT clause
  • ORDER BY clause

For parsing purposes, the query is evaluated in a particular order. For instance, FROM is parsed first followed by WHERE and then followed by GROUP BY and so on.

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