Given the table products(id, name, stock) with rows: (1, 'Pen', 10), (2, 'Pencil', 5), what will be the result of this query?

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PostgreSQL - Common Table Expressions

Given the table products(id, name, stock) with rows: (1, 'Pen', 10), (2, 'Pencil', 5), what will be the result of this query?

WITH updated AS (UPDATE products SET stock = stock + 10 WHERE name = 'Pen' RETURNING *) SELECT * FROM updated;

A[{id:1, name:'Pen', stock:20}]

B[{id:1, name:'Pen', stock:10}]

C[{id:2, name:'Pencil', stock:15}]

DEmpty result set

Step-by-Step Solution

Solution:

Step 1: Identify updated rows
The UPDATE increases stock by 10 only for product with name 'Pen' (id=1), changing stock from 10 to 20.
Step 2: Understand RETURNING and SELECT
The RETURNING * returns the updated row, and the SELECT outputs it.
Final Answer:
[{id:1, name:'Pen', stock:20}] -> Option A
Quick Check:
Updated Pen stock = 10 + 10 = 20 [OK]

Quick Trick: RETURNING shows updated rows immediately [OK]

Common Mistakes:

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