[Solved] Given the table 'orders' with 1 million rows and an index on 'customer_id', what will be the likely effect of this query?SELECT * FROM orders WHERE customer_id = 123; | PostgreSQL

PostgreSQL - Performance Tuning

Given the table 'orders' with 1 million rows and an index on 'customer_id', what will be the likely effect of this query?
SELECT * FROM orders WHERE customer_id = 123;

AThe query will scan the entire table ignoring the index

BThe query will use the index to quickly find matching rows

CThe query will fail due to missing index

DThe query will return no rows because indexes filter data

Step-by-Step Solution

Solution:

Step 1: Understand index usage in WHERE clause
When a column in WHERE has an index, PostgreSQL uses it to find rows faster.
Step 2: Predict query behavior
The query will use the index on customer_id to avoid scanning all rows.
Final Answer:
The query will use the index to quickly find matching rows -> Option B
Quick Check:
Index use in WHERE = Faster row lookup [OK]

Quick Trick: WHERE on indexed column speeds query [OK]

Common Mistakes:

Assuming index is ignored automatically
Thinking index causes query failure
Believing indexes filter out rows

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Given the table 'orders' with 1 million rows and an index on 'customer_id', what will be the likely effect of this query?

Step 1: Understand index usage in WHERE clause

Step 2: Predict query behavior

Final Answer:

Quick Check:

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