[Solved] A developer writes this query:UPDATE customers SET email = 'new@example.com' WHERE id = 123; The email column has an index. The update is very slow. What could be wrong? | SQL

SQL - Indexes and Query Performance

A developer writes this query:

UPDATE customers SET email = 'new@example.com' WHERE id = 123;

The email column has an index. The update is very slow. What could be wrong?

AThe query syntax is invalid and causes a runtime error.

BThe index on <code>email</code> must be updated, causing overhead.

CThe <code>WHERE</code> clause is missing, so all rows are updated.

DThe <code>email</code> column cannot be updated if indexed.

Step-by-Step Solution

Solution:

Step 1: Identify the indexed column being updated
The email column is indexed and is being updated.
Step 2: Understand the impact of updating an indexed column
Updating an indexed column requires updating the index, which adds overhead and slows the query.
Final Answer:
The index on email must be updated, causing overhead. -> Option B
Quick Check:
Index update overhead = slow UPDATE [OK]

Quick Trick: Updating indexed columns adds overhead, slowing queries [OK]

Common Mistakes:

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