SQL | LIKE
Sometimes we may require tuples from the database which match certain patterns. For example, we may wish to retrieve all columns where the tuples start with the letter ‘y’, or start with ‘b’ and end with ‘l’, or even more complicated and restrictive string patterns. This is where the LIKE Clause comes to rescue, often coupled with the WHERE Clause in SQL.
There are two kinds of wildcards used to filter out the results:
- % : Used to match zero or more characters. (Variable Length)
- _ : Used to match exactly one character. (Fixed Length)
The following are the rules for pattern matching with the LIKE Clause:
| Pattern | Meaning |
|---|---|
| ‘a%’ | Match strings which start with ‘a’ |
| ‘%a’ | Match strings with end with ‘a’ |
| ‘a%t’ | Match strings which contain the start with ‘a’ and end with ‘t’. |
| ‘%wow%’ | Match strings which contain the substring ‘wow’ in them at any position. |
| ‘_wow%’ | Match strings which contain the substring ‘wow’ in them at the second position. |
| ‘_a%’ | Match strings which contain ‘a’ at the second position. |
| ‘a_ _%’ | Match strings which start with ‘a’ and contain at least 2 more characters. |
Example:
Say we have a relation, Supplier. We want to test various patterns using the LIKE clause:
Supplier Table:
| SupplierID | Name | Address |
|---|---|---|
| S1 | Paragon Suppliers | 21-3, Okhla, Delhi |
| S2 | Mango Nation | 21, Faridabad, Haryana |
| S3 | Canadian Biz | 6/7, Okhla Phase II, Delhi |
| S4 | Caravan Traders | 2-A, Pitampura, Delhi |
| S5 | Harish and Sons | Gurgaon, NCR |
| S6 | Om Suppliers | 2/1, Faridabad, Haryana |
Sample Queries and Outputs:
SELECT SupplierID, Name, Address FROM Suppliers WHERE Name LIKE 'Ca%';
Output:
| S3 | Canadian Biz | 6/7, Okhla Phase II, Delhi |
| S4 | Caravan Traders | 2-A, Pitampura, Delhi |
SELECT * FROM Suppliers WHERE Address LIKE '%Okhla%';
Output:
| S1 | Paragon Suppliers | 21-3, Okhla, Delhi |
| S3 | Canadian Biz | 6/7, Okhla Phase II, Delhi |
SELECT SupplierID, Name, Address FROM Suppliers WHERE Name LIKE '_ango%';
Output:
| S2 | Mango Nation | 21, Faridabad, Haryana |
Application: The LIKE operator is extremely resourceful in situations such as address filtering wherein we know only a segment or a portion of the entire address (such as locality or city) and would like to retrieve results based on that. The wildcards can be resourcefully exploited to yield even better and more filtered tuples based on the requirement.
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