[Solved] Why does the following query cause an error?SELECT id, name FROM table1 UNION ALL SELECT id FROM table2; | SQL

SQL - Set Operations

Why does the following query cause an error?
SELECT id, name FROM table1 UNION ALL SELECT id FROM table2;

AUNION ALL cannot combine different tables

BUNION ALL requires ORDER BY in both queries

CMissing WHERE clause in second SELECT

DNumber of columns in both SELECTs differ

Step-by-Step Solution

Solution:

Step 1: Check column counts in both SELECTs
First SELECT has 2 columns, second has 1 column.
Step 2: Understand UNION ALL requirements
Both SELECTs must have the same number of columns.
Final Answer:
Number of columns in both SELECTs differ -> Option D
Quick Check:
Column count mismatch causes error [OK]

Quick Trick: UNION ALL requires same number of columns in SELECTs [OK]

Common Mistakes:

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