Single, Double, or Backticks in MySQL: When Should I Use Which?

The clever use of single quotes, double quotes and backticks in MySQL

In MySQL queries, precise referencing is critical to data integrity and accuracy. To avoid confusion, it's important to understand the role of single quotes ('), double quotes ("), and backticks (`).

Backtick: Exclusive symbol for table and column identifiers

Backticks are primarily used to enclose table and column identifiers, especially when the identifier is a MySQL reserved keyword, contains space characters, or uses special characters. This ensures that MySQL interprets them correctly and avoids ambiguity.

Single quotes: the guardian of string values

Single quotes are used to enclose string values ​​in queries. They enclose textual data (such as values ​​in a VALUES() list), ensuring that MySQL interprets the data literally as a string.

Double quotes: alternative for string values ​​

While MySQL supports the use of double quotes for string values, it is recommended to stick to single quotes for consistency and broader compatibility across different relational database management systems (RDBMS).

No quotes required: functions and keywords

MySQL built-in functions (such as NOW()) and reserved keywords (such as NULL) do not require quotes. However, their actual parameters should follow the proper quoting rules for strings or identifiers.

Variable interpolation

When using variable interpolation, use double quotes to enclose PHP strings and single quotes to enclose the string values ​​within to ensure proper variable escaping.

Prepared statements

When using prepared statements, refer to the API documentation to determine whether placeholders need to be quoted. Popular PHP APIs such as PDO and MySQLi expect unquoted placeholders.

Characters that require backtick quoting

In addition to reserved keywords and whitespace, certain characters also require identifiers to be quoted using backticks, including:

• Characters other than the ASCII character set [0-9,a-z,A-Z,$_]
• Identifiers starting with a number

Example

Consider the following query:

<code class="language-sql">INSERT INTO `user` (`id`, `name`, `email`) VALUES (NULL, 'Alice', 'alice@example.com')</code>

Here, user is enclosed in backticks because it is a MySQL keyword. Single quotes enclose 'Alice' and 'alice@example.com' as string values. NULL remains unquoted because it is a special (non-)value.

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