[Solved] Given the table edges(source INT, target INT) with data:(1, 2), (2, 3), (3, 4)What will be the output of this query?... | PostgreSQL

PostgreSQL - Common Table Expressions

Given the table edges(source INT, target INT) with data:
(1, 2), (2, 3), (3, 4)
What will be the output of this query?

WITH RECURSIVE path AS ( SELECT source, target FROM edges WHERE source = 1 UNION ALL SELECT e.source, e.target FROM edges e JOIN path p ON e.source = p.target ) SELECT * FROM path ORDER BY source, target;

A(1,2), (2,3), (3,4)

B(1,2), (2,3)

C(1,2)

D(2,3), (3,4)

Step-by-Step Solution

Solution:

Step 1: Understand anchor member
The anchor selects edges starting at source=1, so (1,2) is included first.
Step 2: Recursive member joins edges where source matches previous target
From (1,2), next edge with source=2 is (2,3), then from (2,3) next is (3,4).
Final Answer:
(1,2), (2,3), (3,4) -> Option A
Quick Check:
Recursive join finds all connected edges from source=1 [OK]

Quick Trick: Recursive CTE follows edges step-by-step from anchor [OK]

Common Mistakes:

Stopping after first recursion
Ignoring recursive join condition
Misreading anchor member

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Given the table edges(source INT, target INT) with data:

Step 1: Understand anchor member

Step 2: Recursive member joins edges where source matches previous target

Final Answer:

Quick Check:

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