[Solved] Consider this SQL query:SELECT a.id, b.value FROM tableA a RIGHT JOIN tableB b ON a.id = b.a_id WHERE a.id > 10;What is the main issue with this query? | SQL

SQL - Advanced Joins

Consider this SQL query:

SELECT a.id, b.value FROM tableA a RIGHT JOIN tableB b ON a.id = b.a_id WHERE a.id > 10;

What is the main issue with this query?

ARIGHT JOIN syntax is incorrect; it should be LEFT JOIN

BThe WHERE clause filters out rows where a.id is NULL, negating the RIGHT JOIN effect

CThe ON condition is invalid because columns have different names

DThe query will cause a syntax error due to aliasing

Step-by-Step Solution

Solution:

Step 1: Understand RIGHT JOIN with WHERE filter
RIGHT JOIN returns all rows from tableB and matching from tableA. Rows with no match have NULL in a.id.
Step 2: Effect of WHERE a.id > 10
The WHERE clause excludes rows where a.id is NULL, removing unmatched rows from tableB, which defeats the purpose of RIGHT JOIN.
Final Answer:
The WHERE clause filters out rows where a.id is NULL, negating the RIGHT JOIN effect -> Option B
Quick Check:
Filtering NULLs after RIGHT JOIN removes unmatched rows [OK]

Quick Trick: Filter NULLs in JOIN condition, not WHERE, to keep unmatched rows [OK]

Common Mistakes:

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