MySQL: Mastering String Concatenation Techniques（mssql字符串连接）

MySQL is one of the most popular databases, and many developers find themselves using it in some capacity. When working with MySQL, it is essential to understand the different techniques for string concatenation in order to make the most of your data. String concatenation is the process of combining two or more strings into a single string, and MySQL provides multiple methods for how to do this. This article explores the different techniques for string concatenation in MySQL and provides practical examples of each.

The simplest way to concatenate strings in MySQL is to use the CONCAT() function. This is the most straightforward way to combine strings and is best used when you need to combine multiple strings into one. The syntax for the CONCAT() function is as follows:

`SELECT CONCAT (string_1, string_2,**string_n**)`

The CONCAT() function takes in any number of strings as arguments and returns the concatenated string. For example, let’s say we have two strings – “Hello” and “World” – and want to concatenate them together. We can use the CONCAT() function like so:

`SELECT CONCAT (“Hello”,”World”)`

Which returns the combined string “HelloWorld”.

In addition to the CONCAT() function, MySQL also provides the || operator for string concatenation. The || operator is a shorthand for the CONCAT() function and allows for quick and easy string concatenation. The syntax for using the || operator is as follows:

`SELECT string_1 || string_2 || string_n`

For example, let’s say we want to combine the same two strings (“Hello” and “World”) as before. We can use the || operator like so:

`SELECT “Hello” || “World”`

Which also returns the combined string “HelloWorld”.

In addition to the CONCAT() and || operators, MySQL also provides the CONCAT_WS() function for string concatenation. This function is similar to the CONCAT() function but provides an additional argument for a separator string that is added between each of the concatenated strings. The syntax for using the CONCAT_WS() function is as follows:

`SELECT CONCAT_WS (separator_string, string_1, string_2, string_n)`

For example, let’s say we have the same two strings (“Hello” and “World”) and want to combine them together with the string ” ” (space) as a separator. We can use the CONCAT_WS() function like so:

`SELECT CONCAT_WS (” “, “Hello”, “World”)`

This returns the combined string “Hello World”.

Finally, while not a technique for string concatenation, MySQL also provides the SUBSTRING() function which allows you to extract a portion of a string. The syntax for the SUBSTRING() function is as follows:

`SELECT SUBSTRING (string, start_position, substring_length)`

For example, let’s say we want to extract the last three characters of the string “HelloWorld”. We can use the SUBSTRING() function like so:

`SELECT SUBSTRING (“HelloWorld”, 8, 3)`

Which returns the result “ld”.

In conclusion, MySQL provides multiple techniques for string concatenation, which can be used depending on the situation. From the simple CONCAT() function to the more advanced CONCAT_WS() and SUBSTRING() functions, it is important to understand the different techniques and how to use them to get the results you need.