# 3.2 Sargability
The most important lesson in database laziness is **Sargability** (Search
ARGument ABLE). It is the art of asking a question in a way that allows the
elephant to use his shortcuts.
## The Peeled Banana (Sargable)
Imagine a perfectly peeled banana sitting on a stool. The elephant can just pick
it up and eat it. When you say `WHERE id = 5`, this is **SARGABLE**. The mouse
librarian can look at the B-Tree and tell the elephant exactly which suitcase to
grab.
## The Banana in the Safe (Non-Sargable)
Now imagine an identical banana locked inside a complex, high-tech steel safe
with a mathematical equation on the door. The elephant cannot eat the banana
until it solves the equation. When you say `WHERE id + 1 = 6`, this is
**NON-SARGABLE**.
Even though _you_ know it means `id=5`, the elephant doesn't take risks. It has
to take _every single suitcase_ in the warehouse, pull out the `id`, add 1 to
it, and see if it equals 6. It cannot use an index because the index is built on
`id`, not on `id + 1`.
## Common Crimes Against Laziness
| Crime | Why it’s Non-Sargable | The Lazy Alternative |
| :-------------------------------------- | :----------------------------------------------- | :--------------------------------------------------------------- |
| `WHERE lower(name) = 'bob'` | Must run `lower()` on every row first. | Use an expression index or `WHERE name = 'Bob'`. |
| `WHERE date + interval '1 day' > now()` | Must do math on every row. | `WHERE date > now() - interval '1 day'`. |
| `WHERE name LIKE '%smith%'` | Cannot use a standard B-Tree for middle-matches. | Use a [[Chapter 2/2.2 - GIN & GiST (The Word Scavenger) |
Remember: if you put a function on the left side of the equals sign, you are
putting a banana in a safe. Don't do that to the elephant.
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[[Chapter 3/3.1 - The Lazy General's Map|← 3.1 - The Lazy General's Map]] | [[Chapter 3/3.0 - The Battle for Efficiency|↑ 3.0 - The Battle for Efficiency]] | [[Chapter 3/3.3 - The Soldiers|3.3 - The Soldiers →]]