When to use single quotes, double quotes, and backticks in MySQL?

MySQL can be particular about quotes and the contexts in which they’re used. Knowing the difference is crucial for writing valid and efficient queries. Below is a quick guide:

1. Single Quotes (' ') for String Literals

In MySQL (and SQL generally), single quotes are used for string literals:

SELECT * 
FROM users
WHERE username = 'alice';

• Required for Strings: Whenever you represent a piece of text, a date, or any non-numeric literal, wrap it in single quotes.
• Escaping Single Quotes: If you need to include a single quote inside the string, you can escape it with a backslash (\').

Example

INSERT INTO messages (id, content) 
VALUES (1, 'It\'s a sunny day!');

2. Double Quotes (" ") for Identifiers (If ANSI_QUOTES Mode is Enabled)

By default, MySQL treats double quotes the same as single quotes—i.e., as string delimiters. However, if you enable the ANSI_QUOTES SQL mode, MySQL will interpret double quotes as identifier delimiters (like backticks). This can be helpful if you’re aiming for more ANSI SQL compliance or working with code ported from databases that follow the SQL standard more strictly.

-- Only works if ANSI_QUOTES is ON
SET sql_mode = 'ANSI_QUOTES';

SELECT "user_id", "created_at"
FROM "orders";

• Potential Confusion: If ANSI_QUOTES is off, then " is treated as a string delimiter. Always check your MySQL server’s SQL mode if you want to use double quotes for identifiers.
• Most Common Practice: In many MySQL environments, double quotes are not used for identifiers. They are simply treated as an alternative for string literals.

3. Backticks (` `) for Identifiers

Backticks are MySQL’s native way of quoting identifiers, including table names, column names, database names, etc.:

SELECT `user_name`, `email`
FROM `user_table`
WHERE `country` = 'USA';

When to Use Backticks

1. Reserved Keywords: If your table or column name is a MySQL reserved word (e.g., group, order, or select), wrapping the identifier in backticks avoids syntax errors.
2. Special Characters: If the name contains spaces or symbols (my table, user-email), backticks let you use these special characters as valid identifier names.
3. Consistent Naming Convention: Even if not strictly necessary, some teams use backticks for clarity and consistency.

Example

CREATE TABLE `order` (
  `id` INT AUTO_INCREMENT PRIMARY KEY,
  `user` VARCHAR(50),
  `status` VARCHAR(20)
);

Without backticks, order might conflict with the SQL keyword ORDER BY.

4. Summary of Usage

1. Single Quotes ' ': String or date literals

   SELECT * FROM users WHERE city = 'New York';

2. Double Quotes " ":

   • By default, acts just like single quotes for strings.
   • If ANSI_QUOTES is enabled: used for identifiers (similar to backticks).

3. Backticks ` `:

   • MySQL’s default identifier delimiter.
   • Use for object names that might otherwise cause syntax errors or confusion.

5. Best Practices

• Avoid Ambiguity: Only use double quotes for identifiers if you’ve explicitly enabled ANSI_QUOTES. Otherwise, stick to backticks.
• Consistent Naming: If possible, avoid naming tables or columns after keywords or including special characters. This can eliminate the need for backticks.
• Always Use Single Quotes for Strings: This is SQL standard and expected behavior across nearly all database systems.

6. Expand Your MySQL Knowledge

To further enhance your database and SQL skills, consider these resources from DesignGurus.io:

• Grokking SQL for Tech Interviews: Go beyond the basics with real-world queries, performance tuning, and advanced SQL interview questions.
• Grokking Database Fundamentals for Tech Interviews: Delve into indexing, normalization, and data modeling best practices essential for large-scale systems.

7. Practice with Mock Interviews

If you want expert feedback on your SQL and database design approach, try Mock Interviews at DesignGurus.io. You’ll get personalized coaching from ex-FAANG engineers, refining both your technical and problem-solving skills.

In conclusion, remember:

1. Use single quotes for string literals (standard practice).
2. Use backticks for identifiers (MySQL’s native style).
3. Use double quotes for identifiers only if ANSI_QUOTES is enabled.

Following these guidelines keeps your queries both portable (where possible) and free from confusing syntax errors. Happy querying!