SQL - Indexes and Query Performance
What will be the outcome if the following SQL command is executed twice?
CREATE INDEX idx_salary ON employees(salary);
What will be the outcome if the following SQL command is executed twice?
medium📝 query result Q5 of 15
Step-by-Step Solution
Solution:
Step 1: Understand Index Creation Behavior
Most SQL databases do not allow creating an index with the same name twice without dropping it first.Step 2: Analyze the Options
The second execution will fail with an error about the index already existing. correctly states that the second attempt will cause an error. Options B, C, and D are incorrect behaviors.Final Answer:
The second execution will fail with an error about the index already existing. -> Option AQuick Check:
Duplicate index names cause errors [OK]
Quick Trick: Index names must be unique; duplicates cause errors [OK]
Common Mistakes:
- Assuming indexes can be created multiple times with same name
- Believing the second command silently succeeds
- Thinking the index is automatically replaced
Master "Indexes and Query Performance" in SQL
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