Rewriting queries
- SQL course
- Expert
- Lesson 22/45
- 5 min
Make the query sargable.
Rewrite the query
In the fourth step you turn a non-sargable condition like DATE(created_at) = '2026-01-01' into a form the index can use: created_at >= ... AND created_at < ....
-- YANLIŞ: WHERE DATE(created_at) = '2026-01-01'
-- DOĞRU: WHERE created_at >= '2026-01-01'
-- AND created_at < '2026-01-02'Sargable uses the index.
Rewrite the query — details
Wrapping a column in a function disables the index. Instead of DATE(created_at) you write a range condition. The index kicks back in and the plan speeds up.
Practice Rewrite the query
Write a sargable query: use created_at >= '2026-01-01' AND created_at < '2026-01-02'.
Starter code
CREATE TABLE orders (
id SERIAL PRIMARY KEY,
customer_id INT,
amount NUMERIC,
created_at TIMESTAMP
);
-- read plan
EXPLAIN SELECT * FROM orders WHERE customer_id = 5;
-- add index
CREATE INDEX idx_orders_customer ON orders (customer_id) INCLUDE (amount);
-- sargable rewrite
SELECT * FROM orders WHERESample solution
CREATE TABLE orders (
id SERIAL PRIMARY KEY,
customer_id INT,
amount NUMERIC,
created_at TIMESTAMP
);
-- read plan
EXPLAIN SELECT * FROM orders WHERE customer_id = 5;
-- add index
CREATE INDEX idx_orders_customer ON orders (customer_id) INCLUDE (amount);
-- sargable rewrite
SELECT * FROM orders WHERE created_at >= '2026-01-01' AND created_at < '2026-01-02';Expected output
Index Scan on orders using idx_orders_customer
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Rewriting queries: match the terms
| Term | Meaning |
|---|---|
sargable |
sargable |
function |
function |
range |
range |
index |
index |
2 Range condition
Question
created_at >= '2026-01-01' AND created_at ____
Answer
created_at >= '2026-01-01' AND created_at < '2026-01-02'Explanation: < '2026-01-02' is the right answer.
3 What does a non-sargable condition do?
- Speeds up the index
- Drops the table
- It adds a column
- Prevents the index from being used Correct answer
Explanation: A non-sargable condition disables the index.