> For the complete documentation index, see [llms.txt](https://docs.prestashop-project.org/1-6-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.prestashop-project.org/1-6-documentation/english-documentation/developer-guide/coding-standards/sql-guidelines.md).
# SQL Guidelines
## Table names
1. Table names must begin with the PrestaShop "`_DB_PREFIX_`" prefix.
```
... FROM `'. _DB_PREFIX_.'customer` ...
```
2. Table names must have the same name as the object they reflect: "`ps_cart`".
3. Table names have to stay singular: "`ps_order`".
4. Language data have to be stored in a table named exactly like the object's table, and with the "`_lang`" suffix: "`ps_product_lang`".
## SQL query
1. Keywords must be written in uppercase.
```
SELECT `firstname`
FROM `'._DB_PREFIX_.'customer`
```
2. Back quotes ("`` ` ``") must be used around SQL field names and table names.
```
SELECT p.`foo`, c.`bar`
FROM `'._DB_PREFIX_.'product` p, `'._DB_PREFIX_.'customer` c
```
3. Table aliases have to be named by taking the first letter of each word, and must be lowercase.
```
SELECT p.`id_product`, pl.`name`
FROM `'._DB_PREFIX_.'product` p
NATURAL JOIN `'._DB_PREFIX_.'product_lang` pl
```
4. When conflicts between table aliases occur, the second character has to be also used in the name.
```
SELECT ca.`id_product`, cu.`firstname`
FROM `'._DB_PREFIX_.'cart` ca, `'._DB_PREFIX_.'customer` cu
```
5. A new line has to be created for each clause.
```
$query = 'SELECT pl.`name`
FROM `'._DB_PREFIX_.'product_lang` pl
WHERE pl.`id_product` = 17';
```
6. It is forbidden to make a `JOIN` in a `WHERE` clause.
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