Rewriting queries

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.

Exercise Rewrite the query

Write a sargable query: use created_at >= '2026-01-01' AND created_at < '2026-01-02'.

Show example 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';

Test yourself

Rewriting queries: match the terms

sargable

sargable
function

function
range

range
index

index

Range condition

created_at >= '2026-01-01' AND created_at ____

Show answer

created_at >= '2026-01-01' AND created_at < '2026-01-02'

What does a non-sargable condition do?
- Speeds up the index
- Drops the table
- It adds a column
- Prevents the index from being used
Show answer

Prevents the index from being used — A non-sargable condition disables the index.

Next lesson: Comparing results

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