In SQL, the LAST_VALUE function is used to retrieve the last value of an expression for each row within a window frame. It is often used in combination with string functions to perform operations on the last value of a string within a group of rows. This can be helpful in various scenarios such as finding the last occurrence of a character or extracting a specific substring from the last value.

Let’s explore some examples of using LAST_VALUE with string functions.

Example 1: Finding the Last Occurrence of a Character

Suppose we have a table called employees with a column called name that contains the full names of employees. We want to find the position of the last occurrence of the letter ‘e’ in each name.

SELECT name, 
    LAST_VALUE(LOCATE('e', name)) OVER (ORDER BY name) AS last_occurrence_of_e
FROM employees;

In this example, we use the string function LOCATE to find the position of ‘e’ in each name. The LAST_VALUE function then retrieves the last occurrence of ‘e’ within the window frame defined by the ORDER BY clause. The result will be a table with two columns: name and last_occurrence_of_e.

Example 2: Extracting a Substring from the Last Value

Let’s suppose we have a table called messages with a column called message that contains text messages. We want to extract the last five characters from each message.

SELECT message, 
    LAST_VALUE(SUBSTRING(message, -5)) OVER (ORDER BY message) AS last_five_characters
FROM messages;

In this example, we use the string function SUBSTRING to extract the last five characters from each message. By providing a negative number as the second argument to SUBSTRING, we ensure that the substring starts from the end of the message. The LAST_VALUE function retrieves the last substring within the window frame defined by the ORDER BY clause. The result will be a table with two columns: message and last_five_characters.

Conclusion

The LAST_VALUE function combined with string functions can be a powerful tool when working with string data in SQL. It allows us to perform operations on the last value within a group of rows, giving us more flexibility and control in our queries.

#sql #stringfunctions