SQL Server String DIFFERENCE() Function

SQL Server DIFFERENCE() Function

The SQL Server DIFFERENCE() function is used to compare the similarity of two strings based on their SOUNDEX values. It returns an integer value between 0 and 4, where 4 indicates the highest similarity. This function is useful for string comparison and matching tasks.

Syntax

SELECT DIFFERENCE(string1, string2);

The DIFFERENCE() function takes two arguments:

  • string1: The first string to compare.
  • string2: The second string to compare.

Example SQL Server DIFFERENCE() Function Queries

Let's look at some examples of SQL Server DIFFERENCE() function queries:

1. Basic DIFFERENCE() Example

SELECT DIFFERENCE('Smith', 'Smyth') AS similarity_score;

This query compares the similarity between the strings 'Smith' and 'Smyth'. The result will be:

similarity_score
----------------
4

2. DIFFERENCE() with Less Similar Strings

SELECT DIFFERENCE('Smith', 'Johnson') AS similarity_score;

This query compares the similarity between the strings 'Smith' and 'Johnson'. The result will be:

similarity_score
----------------
2

3. DIFFERENCE() with Identical Strings

SELECT DIFFERENCE('Database', 'Database') AS similarity_score;

This query compares the similarity between two identical strings 'Database'. The result will be:

similarity_score
----------------
4

Full Example

Let's go through a complete example that includes creating a table, inserting data, and using the DIFFERENCE() function.

Step 1: Creating a Table

This step involves creating a new table named names_table to store some sample data.

CREATE TABLE names_table (
    id INT PRIMARY KEY,
    name1 VARCHAR(50),
    name2 VARCHAR(50)
);

In this example, we create a table named names_table with columns for id, name1, and name2.

Step 2: Inserting Data into the Table

This step involves inserting some sample data into the names_table.

INSERT INTO names_table (id, name1, name2) VALUES (1, 'Smith', 'Smyth');
INSERT INTO names_table (id, name1, name2) VALUES (2, 'Smith', 'Johnson');
INSERT INTO names_table (id, name1, name2) VALUES (3, 'Database', 'Database');

Here, we insert data into the names_table.

Step 3: Using the DIFFERENCE() Function

This step involves using the DIFFERENCE() function to compare the similarity of the names in the name1 and name2 columns.

SELECT id, name1, name2, DIFFERENCE(name1, name2) AS similarity_score
FROM names_table;

This query retrieves the id, name1, name2, and the similarity score for each row in the names_table. The result will be:

id  name1     name2     similarity_score
--- --------- --------- ----------------
1   Smith     Smyth     4
2   Smith     Johnson   2
3   Database  Database  4

Conclusion

The SQL Server DIFFERENCE() function is a powerful tool for comparing the similarity of two strings based on their SOUNDEX values. Understanding how to use the DIFFERENCE() function and its syntax is essential for effective string comparison and matching tasks in SQL Server.