You created a B-tree index on the email column of the users table, but queries filtering by email are still slow. What is a likely cause?
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SQL - Indexes and Query Performance
You created a B-tree index on the email column of the users table, but queries filtering by email are still slow. What is a likely cause?
AThe index was created on the wrong column
BThe query uses a function on <code>email</code> preventing index use
CB-tree indexes do not speed up queries on text columns
DThe table has too few rows for the index to help
Step-by-Step Solution
Solution:
Step 1: Analyze query and index interaction
If the query applies a function (like LOWER(email)) on the indexed column, the B-tree index cannot be used directly.
Step 2: Evaluate other options
The index was created on the wrong column is unlikely if index was created correctly; C is false because B-tree indexes work on text; D is possible but less likely than B.
Final Answer:
The query uses a function on email preventing index use -> Option B
Quick Check:
Functions on indexed columns block B-tree use [OK]
Quick Trick:Functions on indexed columns disable B-tree index use [OK]
Common Mistakes:
Assuming B-tree indexes don't work on text
Ignoring query transformations on columns
Blaming index creation without checking query
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