Common escape characters in MySQL include single quotation mark ('), double quotation mark ("), backslash (), and some special characters, such as percent sign (%) and underscore ( _). These characters have special meaning in MySQL. If not escaped, it may lead to incorrect query results or security issues such as SQL injection.
In MySQL, escape characters can be reversed Escape with slashes. When using single quotes in query statements, you need to add a backslash before the single quotes to escape
SELECT * FROM my_table WHERE my_column = 'I'm a student';
so that you can correctly query the string containing single quotes. Similarly , if you want to use double quotes, you also need to escape them:
SELECT * FROM my_table WHERE my_column = "The book is called "The Great Gatsby"";
In MySQL, backslashes can also be used to escape special characters. You can use the following search statement to query strings containing percent signs
SELECT * FROM my_table WHERE my_column LIKE '%%%';
This way you can correctly match the percent sign in the string.
MySQL provides some built-in functions that can be used to escape characters, not limited to using backslash to escape characters In this way. For example, you can use the double vertical bar (||) operator to connect strings, and use the function CONCAT_WS() to automatically escape characters, as shown below:
SELECT CONCAT_WS(' ', 'I', 'am', 'a', 'student') AS sentence;
This query statement will return a A string containing spaces in which words have been properly escaped.
To prevent security issues with string injection, not only can escape characters be used to escape strings, but parameterization can also be used Query method. Parameterized queries that use placeholders instead of actual values can prevent the database from being attacked by malicious users injecting malicious strings. For example, you can use the following parameterized query to query strings containing specified words:
SELECT * FROM my_table WHERE my_column LIKE CONCAT('%', ?, '%');
The question mark here represents a placeholder that can be dynamically replaced with the actual value during query. Using parameterized queries can greatly improve the security of the application.
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