[Solved] You wrote this SQL query but it throws an error: SELECT * FROM ( SELECT id, name FROM users ) AS user_sub WHERE user_sub.age > 30; What is the most likely cause of the error? | SQL

SQL - Common Table Expressions (CTEs)

You wrote this SQL query but it throws an error:

SELECT * FROM (
  SELECT id, name FROM users
) AS user_sub WHERE user_sub.age > 30;

What is the most likely cause of the error?

AThe subquery alias 'user_sub' is missing

BThe WHERE clause should be inside the subquery

CThe subquery does not include the 'age' column needed in WHERE

DSubqueries cannot be used in FROM clause

Step-by-Step Solution

Solution:

Step 1: Check subquery columns
The subquery selects only 'id' and 'name' columns, but the outer query filters on 'age' which is not selected.
Step 2: Understand SQL column visibility
Since 'age' is not in the subquery result, the outer WHERE clause referencing 'age' causes an error.
Final Answer:
The subquery does not include the 'age' column needed in WHERE -> Option C
Quick Check:
Missing column in subquery causes error [OK]

Quick Trick: Ensure subquery selects all columns used outside [OK]

Common Mistakes:

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