Db2 SUBSTRING

Summary: in this tutorial, you will learn how to use the Db2 SUBSTRING() function to extract a substring from a string.

Db2 SUBSTRING() function overview

The SUBSTRING() function allows you to extract a substring from a string. The basic syntax of the SUBSTRING() function is the following:

SUBSTRING( source_string, start_position [, substring_length ] );

The SUBSTRING() function returns a substring from the source_string starting at start_position with the substring_length length.

The following explains the meanings of the three arguments:

 source_string

The source_string is the source string from which you want to extract a substring.

 start_position

The start_position is a positive integer that specifies the location where the substring starts.

 substring_length

The substring_length specifies the number of characters of the substring to be extracted.

If you skip the substring_length, the function returns the rest of the source_string starting from the start_position location.

Db2 SUBSTRING() function examples

Let’s take some examples of using the SUBSTRING() function to understand it better.

1) Using Db2 SUBSTRING() function to extract a substring example

This example uses the SUBSTRING() function to extract a substring whose length is 3 starting from the first character of the source string:

SELECT
    SUBSTRING( 'Db2 Substring', 1, 3 ) Result
FROM
    sysibm.sysdummy1;

Here is the output:

RESULT     
------------- 
Db2        

2) Using Db2 SUBSTRING() function with no substring’s length argument example

This example extracts a substring from the fifth position of the string 'Db2 Substring' to the rest of the string.

SELECT
    SUBSTRING( 'Db2 Substring', 5 ) Result
FROM
    sysibm.sysdummy1;

The following shows the output:

RESULT        
------------- 
Substring   

3) Using Db2 SUBSTRING() function with table data example

Consider the following authors table in the sample database:

This example uses the SUBSTRING() to extract the initials of the author’s last names and the initial count for each initial.

SELECT
    SUBSTRING( first_name, 1, 1 ) initials ,
    COUNT(*)  initial_count
FROM
    authors
GROUP BY
    SUBSTRING( first_name, 1, 1 )
ORDER BY
    initials;

This picture shows the partial result set:

In this tutorial, you have learned how to use the Db2 SUBSTRING() function to extract a substring from a string.