MySQL LEFT() Function

  1. Overview
  2. MYSQL
  3. String Functions
  4. MySQL LEFT() Function

The LEFT() function in MySQL is used to extract a specified number of characters from the start (left) of a string.

Syntax

LEFT(string, number_of_chars)

Parameters

Parameter Description
string Required. The string to extract characters from.
number_of_chars Required. The number of characters to extract from the left of the string.

Definition and Use

  • Purpose: Returns the specified number of characters from the beginning of a string.
  • Behavior:
    • If number_of_chars exceeds the length of the string, the entire string is returned.
    • If number_of_chars is 0, an empty string is returned.

Usage Examples

Example 1: Basic Extraction

Extract 3 characters from the string "SQL Tutorial":

SELECT LEFT("SQL Tutorial", 3) AS ExtractString;

Output:

ExtractString
SQL

Example 2: Extraction from a Column

Extract the first 5 characters from the CustomerName column:

SELECT CustomerName, LEFT(CustomerName, 5) AS ExtractString
FROM Customers;

Output (example data):

CustomerName ExtractString
John Smith John
Alice Brown Alice

Example 3: number_of_chars Exceeds String Length

Extract 15 characters from "SQL" (string length is 3):

SELECT LEFT("SQL", 15) AS ExtractString;

Output:

ExtractString
SQL

Explanation: The length of "SQL" is less than 15, so the entire string is returned.

Example 4: number_of_chars is 0

Extract 0 characters from "SQL Tutorial":

SELECT LEFT("SQL Tutorial", 0) AS ExtractString;

Output:

ExtractString
(empty string)

Technical Details

  • Availability: Available from MySQL 4.0 onwards.
  • Return Type: Returns a string with the extracted characters.

Applications

  1. Substring Extraction: Use LEFT() to retrieve the beginning portion of strings.
  2. Data Transformation: Extract prefixes, initials, or specific parts of text data.
  3. Formatting: Simplify or shorten strings for display or reporting.

Related Functions

  • RIGHT(): Extracts characters from the end of a string.
  • SUBSTRING(): Extracts a substring from a string starting at any position.

Key Notes

  • Ensure number_of_chars is a non-negative integer. Negative values result in an error.
  • For multi-byte characters (e.g., Unicode), ensure proper handling using character set configurations.

The LEFT() function is a versatile tool for extracting text from the beginning of strings, making it essential for text processing in MySQL.

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