[Solved] Why does this self join query cause an error?SELECT e1.name, e2.name FROM employees e1 JOIN employees e2 ON e1.manager_id = e2.id WHERE e1.manager_id = e2.manager_id; | PostgreSQL

PostgreSQL - Joins in PostgreSQL

Why does this self join query cause an error?

SELECT e1.name, e2.name FROM employees e1 JOIN employees e2 ON e1.manager_id = e2.id WHERE e1.manager_id = e2.manager_id;

AWHERE clause references columns ambiguously causing error

BMissing alias for employees table

CNo error, query runs fine

DON clause is invalid syntax

Step-by-Step Solution

Solution:

Step 1: Verify syntax and column references
All columns are fully qualified with table aliases (e1.manager_id = e2.manager_id), no ambiguity.
Step 2: Confirm query executes
The JOIN with ON and WHERE clause are syntactically valid; it may return no rows depending on data but does not error.
Final Answer:
No error, query runs fine -> Option C
Quick Check:
Fully qualified columns = No syntax error [OK]

Quick Trick: Fully qualified columns in WHERE prevent ambiguity [OK]

Common Mistakes:

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Why does this self join query cause an error?