How the QUOTE() function works in Mariadb?

The QUOTE() function is a string function in Mariadb that returns a single-quoted string that is safe to use in a SQL statement. The function escapes any special characters, such as single quotes, backslashes, or control characters, by adding a backslash before them. The function can be used to prevent SQL injection attacks, or to handle user input that may contain special characters.

Syntax

The syntax of the QUOTE() function is as follows:

QUOTE(string)

The function takes one argument:

• string: A string expression that represents the string to be quoted. The string expression can be any valid value, such as a literal, a column, a function, or a variable. The string expression can be NULL.

The function returns a string that represents the quoted string, as follows:

• If the string expression is not NULL, the function returns a single-quoted string that is safe to use in a SQL statement. The function escapes any special characters, such as single quotes, backslashes, or control characters, by adding a backslash before them. For example, QUOTE('O\'Reilly') returns 'O\'Reilly'.
• If the string expression is NULL, the function returns the word NULL without quotes. For example, QUOTE(NULL) returns NULL.

Examples

Example 1: Quoting a string with special characters

The following example quotes a string that contains a single quote and a backslash using the QUOTE() function.

SELECT QUOTE('It\'s a \\test') AS quoted_string;

The output is:

+------------------+
| quoted_string    |
+------------------+
| 'It\'s a \\test' |
+------------------+

The output shows that the QUOTE() function returns a single-quoted string that escapes the single quote and the backslash by adding a backslash before them.

Example 2: Quoting a string with control characters

The following example quotes a string that contains a newline and a tab character using the QUOTE() function.

SELECT QUOTE('Hello\nWorld\t!') AS quoted_string;

The output is:

+-----------------+
| quoted_string   |
+-----------------+
| 'Hello
World	!' |
+-----------------+

The output shows that the QUOTE() function returns a single-quoted string that escapes the newline and the tab character by adding a backslash before them.

Example 3: Quoting a string that is NULL

The following example quotes a string that is NULL using the QUOTE() function.

SELECT QUOTE(NULL) AS quoted_string;

The output is:

+---------------+
| quoted_string |
+---------------+
| NULL          |
+---------------+

The output shows that the QUOTE() function returns the word NULL without quotes, as the string expression is NULL.

Related Functions

There are some other functions that are related to the QUOTE() function, such as:

• CONCAT(): This function returns a string that is the concatenation of two or more string expressions. The syntax of the function is CONCAT(string1, string2, ...), where string1, string2, etc. are string expressions. The function returns a string that is the result of joining the string expressions. For example, CONCAT('Hello', ' ', 'World') returns 'Hello World'.
• REPLACE(): This function returns a string that is the result of replacing all occurrences of a substring within a string with another substring. The syntax of the function is REPLACE(string, from_string, to_string), where string is the original string, from_string is the substring to be replaced, and to_string is the substring to replace with. The function returns a string that is the result of the replacement. For example, REPLACE('Hello World', 'o', 'a') returns 'Hella Warld'.
• SUBSTRING(): This function returns a substring of a string that starts from a specified position and has a specified length. The syntax of the function is SUBSTRING(string, position, [length]), where string is the original string, position is the starting position of the substring, and length is an optional parameter that specifies the length of the substring. The function returns a string that is the substring of the original string. For example, SUBSTRING('Hello World', 7, 5) returns 'World'.

Conclusion

The QUOTE() function is a useful function to return a single-quoted string that is safe to use in a SQL statement. The function escapes any special characters, such as single quotes, backslashes, or control characters, by adding a backslash before them. The function can be used to prevent SQL injection attacks, or to handle user input that may contain special characters. The function takes one argument, which is a string expression that represents the string to be quoted. The function returns a string that represents the quoted string, as follows:

• If the string expression is not NULL, the function returns a single-quoted string that escapes any special characters by adding a backslash before them.
• If the string expression is NULL, the function returns the word NULL without quotes.

The function can also be combined with other string functions, such as CONCAT(), REPLACE(), SUBSTRING(), etc., to perform more complex operations on strings.