What is the difference between single and double quotes in SQL?

sql

best-practices

sql-standards

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byNikita Barsukov·Sep 11, 2024

Primarily, single quotes '' are utilized to encapsulate string literals like 'Hello, World!' or date values such as '2022-12-31'. Double quotes "" are typically delegated for distinguishing database objects like columns or tables which may contain special characters or utilize mixed case, e.g., "myColumn" or "MyTable". This type of double-quote usage adheres to the SQL standard, however, how it's implemented can vary. For instance, in SQLite and PostgreSQL, "DoubleQuotes" are used to strictly preserve the case, whereas in MySQL, double and single quotes can be interchangeable in the default SQL mode.

Example:

SELECT 'I am literal!', "No one can touch my capitalization" FROM "Cant_TouchThis";

Single quotes vs. Double quotes in SQL: Synonyms or Frenemies?

Expressing the literal truth with Single quotes

In SQL, if you wish to express literal values - whether it's a simple string like 'Coding is fun' or conveying a Docker container's birthday '2023-12-31', single quotes are your stalwart companions. You can always rely on them to have your literals' back.

Double quotes: Preserving the identity of Database Objects

However, when it's time to refer to database objects like columns or tables that like flaunting special characters or enjoy the thrill of mixed casing, double quotes step in. For example, "Employee ID" or "Monthly-Data2023".

SQL Platform differences: Double or nothing?

While these rules are generally globally recognized, some SQL platforms like to march to the beat of their own drum. SQL Server and Sybase, prefer to use square brackets [] for identifiers. MySQL and MariaDB on the other hand, roll with backticks `. However, according to the ANSI SQL standards, double quotes signify database object identifiers.

Playing it safe with SQL standards

Although some SQL platforms allow you to devil-may-care about these quote rules, it's a reliable practice to adhere to the standards. This ensures your SQL scripts can navigate different systems flawly, making them more portable.

Diving deeper: Exceptions & Special cases

Special characters and keywords: Double quotes to the rescue!

SQL identifiers sporting special characters or dressing up as reserved keywords? Encase them in double quotes:

SELECT "user$id", "ForgetAboutDre" FROM "my$table"; -- Dr. Dre approved! 😉

Case-sensitive identifiers: PostgreSQL's POV

PostgreSQL loves to keep things lower-case when it comes to identifiers, unless they're swaddled in double quotes. If you create a table "CapitalIdea", referring to it as capitalidea simply won't do!

SELECT * FROM "CapitalIdea"; -- Chilling on cloud nine! 😎
SELECT * FROM CapitalIdea; -- Crash and burn! 🔥

SQL Modes and Quote rules: Setting boundaries

The SQL mode in MySQL or the QUOTED_IDENTIFIER option in SQL Server grant you the power to govern how your database interprets quotes:

MySQL: SET GLOBAL SQL_MODE=ANSI_QUOTES;
SQL Server: SET QUOTED_IDENTIFIER ON;

Once set, double-quote usage is confined to identifying objects, establishing synchronicity with ANSI standards.

Interchangeability woes: MySQL caution

Whilst MySQL’s quote switching ability is undeniably convenient, beware! It’s a double-edged sword that could lead to unforeseen bugs. If ANSI_QUOTES is enabled, using double quotes around string literals is a recipe for disaster:

SELECT "Houston we have a problem!" FROM my_table; -- It's raining errors if ANSI_QUOTES is enabled! ☔
SELECT 'Clear skies ahead!' FROM my_table;

Column aliases: The Single Quote rule

When crafting aliases in SQL, best keep them free of spaces. But if your alias is in the mood to play twister and space is an absolute must, use double quotes:

SELECT column_name AS "Space: The final frontier" FROM my_table; -- Star Trek would be proud! 🚀
SELECT column_name AS Single_Word FROM my_table; -- Boring, but hey it's functional! 🤓