When working with databases, we often face a common problem:
Names or words are spelled differently but sound the same.
For example:
- Smith vs. Smyth
- Mohammad vs. Muhammad
In SQL Server, the SOUNDEX function helps us deal with this by finding words that “sound” alike.
What is SOUNDEX?
SOUNDEX is a phonetic algorithm that converts a string into a 4-character code based on how it sounds in English.
- The first letter is preserved.
- Consonant sounds are mapped to digits.
- Vowels are mostly ignored.
Example:
SELECT SOUNDEX('Smith'), SOUNDEX('Smyth');
Output: Both return S530
Basic Usage
Here’s how you can use SOUNDEX in a real query:
SELECT Name
FROM Customers
WHERE SOUNDEX(Name) = SOUNDEX('Smyth');
This will return names like:
- Smith
- Smyth
- Smithe
Practical Use Cases
Searching customer names
Handle variations like Mohammad, Mohamed, Muhamad.Address search
Match city names like Teheran vs. Tehran.Data cleansing
Detect and merge duplicate records.Search experience in apps
Show results even when the user misspells a word.
Limitations
- Works well for English words, but not for Persian, Arabic, or other languages.
- Not always accurate — sometimes very different words map to the same code.
- For more precise results, you can use
DIFFERENCE, Full-Text Search, or advanced algorithms like Levenshtein distance.
Bonus: Using DIFFERENCE
SQL Server provides another function: DIFFERENCE.
It compares two SOUNDEX values and gives a score between 0 (no similarity) and 4 (strong match).
SELECT DIFFERENCE('Smith', 'Smyth'); -- Returns 4
Conclusion
SOUNDEX in SQL Server is a quick way to perform fuzzy searches and find similar-sounding words.
It’s very useful for:
- Customer name search
- CRM systems
- Data cleansing
But remember, it’s not perfect. For better accuracy, combine it with DIFFERENCE or more advanced text similarity methods.
I’m Morteza Jangjoo and “Explaining things I wish someone had explained to me”
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