LEFT (Transact-SQL)

Άρθρο
09/03/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric

Returns the left part of a character string with the specified number of characters.

Transact-SQL syntax conventions

Syntax

LEFT ( character_expression , integer_expression )

Arguments

character_expression
Is an expression of character or binary data. character_expression can be a constant, variable, or column. character_expression can be of any data type, except text or ntext, that can be implicitly converted to varchar or nvarchar. Otherwise, use the CAST function to explicitly convert character_expression.

Note

If string_expression is of type binary or varbinary, LEFT will perform an implicit conversion to varchar, and therefore will not preserve the binary input.

integer_expression
Is a positive integer that specifies how many characters of the character_expression will be returned. If integer_expression is negative, an error is returned. If integer_expression is type bigint and contains a large value, character_expression must be of a large data type such as varchar(max).

The integer_expression parameter counts a UTF-16 surrogate character as one character.

Return Types

Returns varchar when character_expression is a non-Unicode character data type.

Returns nvarchar when character_expression is a Unicode character data type.

Remarks

When using SC collations, the integer_expression parameter counts a UTF-16 surrogate pair as one character. For more information, see Collation and Unicode Support.

Examples

A. Using LEFT with a column

The following example returns the five leftmost characters of each product name in the Product table of the AdventureWorks2022 database.

SELECT LEFT(Name, 5)   
FROM Production.Product  
ORDER BY ProductID;  
GO

B. Using LEFT with a character string

The following example uses LEFT to return the two leftmost characters of the character string abcdefg.

SELECT LEFT('abcdefg',2);  
GO

Here's the result set.

--   
ab   
  
(1 row(s) affected)

Examples: Azure Synapse Analytics and Analytics Platform System (PDW)

C. Using LEFT with a column

The following example returns the five leftmost characters of each product name.

-- Uses AdventureWorks  
  
SELECT LEFT(EnglishProductName, 5)   
FROM dbo.DimProduct  
ORDER BY ProductKey;

D. Using LEFT with a character string