The MySQL LEFT function is part of string functions and is used to extract a specified number of characters from the left side of a string. It is a powerful function for manipulating and filtering data, and it is commonly used in various scenarios, including:

Substring Extraction: The LEFT() function is ideal for extracting parts of strings based on their leftmost characters. For instance, you could extract the first three letters of a customer’s name to use as a unique identifier.

Data Truncation: The LEFT() function can be used to truncate or limit the length of a string by extracting only a certain number of characters. This is useful for displaying shorter versions of text fields or for handling data that has a specified maximum length.

Data Manipulation: LEFT() is often employed to modify the content of a string by extracting and manipulating its leftmost characters. For example, you could remove the first two characters from a phone number to ensure compatibility with a specific format.

Syntax

The syntax for the LEFT function is as follows:

LEFT(str, length)

str: This is the input string from which you want to extract characters.
length: This is the number of characters to extract from the left side of the input string.

Example

Here’s an example to illustrate the usage of the LEFT function:

SELECT LEFT('MySQL LEFT function', 5) AS Result;

In this example, the result would be the first 5 characters from the left side of the string, which is ‘MySQL’.

You can also use a column name instead of a string literal, making it useful for extracting a specific number of characters from a column in a table:

SELECT LEFT(column_name, 3) AS Result FROM your_table;

This query would extract the first 3 characters from the specified column in the table.

It’s important to note that if the specified length is greater than the length of the string, the entire string will be returned. Additionally, if the length is negative or zero, an empty string will be returned.

Comparison with RIGHT Function

The RIGHT function works similarly to the LEFT function, but it extracts characters from the right side of the string instead of the left side. The syntax and usage of the two functions are identical.

Conclusion

The MySQL LEFT function is a fundamental string manipulation function that allows you to extract specific characters from the left side of a string. It’s widely used for data truncation, data extraction, and string manipulation in MySQL queries.