[Solved] You wrote this query in PostgreSQL 11:WITH cte AS (SELECT id, name FROM users WHERE active = true) SELECT * FROM cte WHERE name LIKE 'A%';The query runs slower than expected. What is a likely cause? | PostgreSQL

PostgreSQL - Common Table Expressions

You wrote this query in PostgreSQL 11:

WITH cte AS (SELECT id, name FROM users WHERE active = true) SELECT * FROM cte WHERE name LIKE 'A%';

The query runs slower than expected. What is a likely cause?

AThe CTE syntax is incorrect and causes a syntax error.

BThe LIKE operator is not supported inside CTEs.

CCTE materialization prevents planner optimizations on the WHERE clause.

DPostgreSQL does not support filtering after CTEs.

Step-by-Step Solution

Solution:

Step 1: Identify CTE behavior in PG11
CTEs are materialized, so filtering after the CTE cannot be pushed down into the CTE query.
Step 2: Understand impact on performance
This prevents the planner from optimizing the WHERE clause inside the CTE, causing slower execution.
Final Answer:
CTE materialization prevents planner optimizations on the WHERE clause. -> Option C
Quick Check:
CTE materialization blocks filter pushdown [OK]

Quick Trick: Filters after CTEs can't optimize inside CTE before PG12 [OK]

Common Mistakes:

Thinking LIKE is unsupported in CTEs
Assuming syntax error causes slowness
Believing filtering after CTE is disallowed

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You wrote this query in PostgreSQL 11:

Step 1: Identify CTE behavior in PG11

Step 2: Understand impact on performance

Final Answer:

Quick Check:

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