SQL Server String LEFT() Function

SQL Server LEFT() Function

The SQL Server LEFT() function is used to extract a specified number of characters from the left side of a string. This function is useful for string manipulation tasks, such as extracting substrings from a larger string.

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Syntax

SELECT LEFT(string, number_of_characters);

The LEFT() function takes two arguments:

• string: The string from which to extract characters.
• number_of_characters: The number of characters to extract from the left side of the string.

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Example SQL Server LEFT() Function Queries

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

1. Basic LEFT() Example

SELECT LEFT('Hello World', 5) AS result;

This query extracts the first 5 characters from the string 'Hello World'. The result will be:

result
------
Hello

2. LEFT() with a Column

SELECT first_name, LEFT(first_name, 3) AS short_name
FROM employees;

This query extracts the first 3 characters from the first_name column for each employee. The result will show the first_name and the extracted substring as short_name.

3. LEFT() with a Variable

DECLARE @myString VARCHAR(50);
SET @myString = 'SQL Server';
SELECT LEFT(@myString, 3) AS result;

This query uses a variable to store a string and then extracts the first 3 characters from it. The result will be:

result
------
SQL

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Full Example

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

Step 1: Creating a Table

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

CREATE TABLE example_table (
    id INT PRIMARY KEY,
    description VARCHAR(50)
);

In this example, we create a table named example_table with columns for id and description.

Step 2: Inserting Data into the Table

This step involves inserting some sample data into the example_table.

INSERT INTO example_table (id, description) VALUES (1, 'Apple');
INSERT INTO example_table (id, description) VALUES (2, 'Banana');
INSERT INTO example_table (id, description) VALUES (3, 'Cherry');

Here, we insert data into the example_table.

Step 3: Using the LEFT() Function

This step involves using the LEFT() function to extract characters from the description column.

SELECT id, description, LEFT(description, 3) AS short_description
FROM example_table;

This query retrieves the id, description, and the first 3 characters of the description column for each row in the example_table. The result will be:

id  description  short_description
--- ------------ ----------------
1   Apple        App
2   Banana       Ban
3   Cherry       Che

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Conclusion

The SQL Server LEFT() function is a powerful tool for extracting a specified number of characters from the left side of a string. Understanding how to use the LEFT() function and its syntax is essential for effective string manipulation and data processing in SQL Server.