How to translate strings in MSSQL in php

It is a common thing for PHP to connect to MSSQL server, but when translating strings, various problems are often encountered. This article will discuss how to correctly define and translate strings in MSSQL in PHP.

1. The difference between String and Varchar

In SQL Server, when defining the string type, you can use char, varchar and nvarchar types. Among them, the char type defines fixed-length strings, and varchar and nvarchar define variable-length strings.

In PHP, string variables are usually used to process text data, and String Length is usually called the string length or the number of words. The way string length is expressed in PHP is based on the number of internally encoded bytes, not the number of characters in the string.

When PHP is connected to the MSSQL server, character encoding conversion is usually used because the character encodings between them are different. When passing strings between PHP and MSSQL, the string encoding should be utf-8, otherwise character set incompatibility problems will occur.

2. String translation in MSSQL

When constructing SQL queries from user input, strings must be handled with caution. Failure to perform proper string escaping could allow attackers to add malicious code to SQL queries. To avoid this situation, MSSQL provides an escape function: REPLACE. The REPLACE function replaces SQL reserved characters (such as single quotes, double quotes, and backslashes) with double reserved characters so that they can be included in SQL queries as part of a string.

Let’s take an example of a case where escaping does not work properly:

$query = "SELECT * FROM exampleTable WHERE name = '$_POST[name]'";

When executing this query, if the value entered by the user contains single quotes, a SQL injection attack will occur. .

The solution to this situation is to use the REPLACE function to escape the string before inserting it into the SQL statement.

$name = str_replace("'", "''", $_POST['name']);
$query = "SELECT * FROM exampleTable WHERE name = '$name'";

The str_replace function here replaces the single quotes in the input with two single quotes before inserting them into the SQL statement. This way you can avoid SQL injection attacks.

3. String translation in PHP

In PHP, you can use the addslashes function to escape strings. This function will escape all special characters such as single quotes, double quotes, backslashes, etc. into characters preceded by a backslash.

For example:

$str = "I'm a string with 'special' characters";
$str = addslashes($str);
echo $str;

The output result is:

I\'m a string with \'special\' characters

In versions above PHP 5.4.0, the addslashes function has been marked as a deprecated function. Instead use mysqli_escape_string() or PDO's prepared statements feature. The mysqli_escape_string() function can escape special characters with meaning in SQL statements and retain them as string literals. When these string literals are used in SQL statements, the MySQL server will interpret them as plain text strings, and Not part of the SQL command. This avoids SQL injection attacks.

Summary

When PHP is connected to the MSSQL server, string escaping is an essential part. When performing string operations, you should try to avoid using direct user input. If you want to use user input to construct a SQL query, you must use the REPLACE function, the mysqli_escape_string() function, or PDO's prepared statements function to escape the string to avoid SQL injection attacks. In addition, the definition of String and Varchar types must also be carefully considered and matched with the string length processing rules in PHP to avoid unexpected escaping problems.

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