SQLServer CONCAT function

        In SQL Server, the CONCAT function is used to concatenate two or more strings together and return a new string. Any number of strings can be concatenated together, and can contain any type of string, including constants, variables, column names, and the results of other functions.

CONCAT ( string1, string2 [, stringN ] )

        ​​​​In SQL Server, the advantages of using CONCATfunctions over directly using +operators to concatenate strings are as follows:

1. Handling of NULL values: +When using operators to concatenate strings, if one of the strings is NULL, the result of the entire expression will also be NULL. When using CONCATa function to concatenate strings, if any parameter is NULL, CONCATthe result of the function will also be NULL. This handling is more intuitive and avoids unexpected NULL values.

2. Performance optimization: In some cases, using CONCATfunctions can be +faster than using operators. The reason is that when using +operators to concatenate strings, SQL Server will concatenate the strings into one string and return the result. When using CONCATthe function to concatenate strings, SQL Server will first concatenate the first string with the second string, then concatenate the result with the third string, and so on, until all strings are concatenated. This approach improves performance by reducing the number of strings that need to be concatenated at each concatenation.

3. Readability and maintainability: Using CONCATfunction concatenation strings can make SQL queries easier to understand and maintain. When concatenating multiple strings, use CONCATfunctions to clearly show how each string is concatenated. Additionally, CONCATfunctions allow strings to be concatenated with the results of other functions, which can make queries more flexible.

        Instructions:

SELECT CONCAT(1,2,3)

        result: