PostgreSQL - Common Table Expressions
What will be the output of this query?
WITH cte1 AS (SELECT 10 AS val), cte2 AS (SELECT val * 2 AS val FROM cte1) SELECT * FROM cte2;
What will be the output of this query? WITH cte1 AS (SELECT 10 AS val), cte2 AS (SELECT val * 2 AS val FROM cte1) SELECT * FROM cte2;
medium📝 query result Q4 of 15
Step-by-Step Solution
Solution:
Step 1: Evaluate cte1
cte1 returns a single row with val = 10.Step 2: Evaluate cte2 using cte1
cte2 multiplies val by 2, so val = 20.Final Answer:
val 20 -> Option CQuick Check:
CTE chaining doubles value = 20 [OK]
Quick Trick: Each CTE can use previous CTEs as tables [OK]
Common Mistakes:
- Confusing which CTE is used in calculation
- Expecting cte1 output instead of cte2
- Assuming multiplication by 3
Master "Common Table Expressions" in PostgreSQL
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