Comparing LIKE vs LEFT for Column Comparisons

SQL SERVER – Comparing LIKE vs LEFT for Column Comparisons

When working with SQL Server, you'll often find yourself needing to compare values in your database columns. Two commonly used methods for such comparisons are the `LIKE` operator and the `LEFT` function. In this blog, we'll explore the differences between these two approaches and when to use each one. To make our exploration more engaging, let's create a hypothetical scenario and some dummy data to work with.

Setting the Stage

Suppose we're managing a fictional online bookstore, and we have a table called `Books` with the following sample data:

CREATE TABLE Books (

BookID INT PRIMARY KEY,

Title NVARCHAR(100),

Author NVARCHAR(100),

PublicationYear INT

);

INSERT INTO Books (BookID, Title, Author, PublicationYear)

VALUES

(1, 'The Catcher in the Rye', 'J.D. Salinger', 1951),

(2, 'To Kill a Mockingbird', 'Harper Lee', 1960),

(3, '1984', 'George Orwell', 1949),

(4, 'Pride and Prejudice', 'Jane Austen', 1813),

(5, 'The Hobbit', 'J.R.R. Tolkien', 1937);

Now, let's assume you need to find all books written by authors whose names start with the letter "J."

Using `LIKE` Operator

The `LIKE` operator is a pattern-matching operator that allows you to search for a specified pattern in a column. In our case, we can use it to find books by authors whose names start with "J."

SELECT * FROM Books

WHERE Author LIKE 'J%';

The `%` symbol is used as a wildcard to match any sequence of characters following the 'J.' This query will return the following result:

| BookID | Title | Author | PublicationYear |

|-----------|-------------------------------|-------------------|-----------------|

| 1                   | The Catcher in the Rye                | J.D. Salinger              | 1951                        |

| 5                  | The Hobbit                                     | J.R.R. Tolkien             | 1937                       |

The `LIKE` operator is quite handy for simple pattern matching, especially when you're looking for values that start with, end with, or contain a specific pattern.

Using `LEFT` Function

The `LEFT` function, on the other hand, extracts a specified number of characters from a string, starting from the left. In our scenario, you can use it to extract the first character from the `Author` column and compare it with "J."

SELECT * FROM Books

WHERE LEFT(Author, 1) = 'J';

This query will also return the same result as before:

| BookID | Title | Author | PublicationYear |

|-----------|-----------------------------|---------------------|-----------------|

| 1                   | The Catcher in the Rye            | J.D. Salinger                  | 1951                       |

| 5                  | The Hobbit                                 | J.R.R. Tolkien                 | 1937                      |

The `LEFT` function is beneficial when you need to extract a specific portion of a string to compare. It offers more control over the extraction process.

Which One to Choose?

- Use `LIKE` when you need to search for patterns within a column and when you want to match substrings with wildcards. It's more flexible for complex pattern matching.

- Use `LEFT` when you need to extract a specific part of a string for comparison. It can be more efficient in cases where you only need to compare the starting characters.

Remember that when dealing with large datasets, the performance of your queries should be a key consideration. Ensure that your choice aligns with your performance goals and the specific needs of your application.