Page 33 - SQL

Chapter 6: Clean Code in SQL

Introduction

How to write good, readable SQL queries, and example of good practices.

Examples

Formatting and Spelling of Keywords and Names

Table/Column Names

Two common ways of formatting table/column names are CamelCase and snake_case:

SELECT FirstName, LastName
FROM Employees
WHERE Salary > 500;

SELECT first_name, last_name
FROM employees
WHERE salary > 500;

Names should describe what is stored in their object. This implies that column names usually
should be singular. Whether table names should use singular or plural is a heavily discussed
question, but in practice, it is more common to use plural table names.

Adding prefixes or suffixes like tbl or col reduces readability, so avoid them. However, they are
sometimes used to avoid conflicts with SQL keywords, and often used with triggers and indexes
(whose names are usually not mentioned in queries).

Keywords

SQL keywords are not case sensitive. However, it is common practice to write them in upper case.

SELECT *

SELECT * returns all columns in the same order as they are defined in the table.

When using SELECT *, the data returned by a query can change whenever the table definition
changes. This increases the risk that different versions of your application or your database are
incompatible with each other.

Furthermore, reading more columns than necessary can increase the amount of disk and network
I/O.

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