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ELSE (IF...ELSE) (Transact-SQL)

  • Άρθρο

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 SQL database in Microsoft Fabric

Imposes conditions on the execution of a Transact-SQL statement. The Transact-SQL statement (sql_statement) following the boolean_expression is executed if the boolean_expression evaluates to TRUE. The optional ELSE keyword is an alternate Transact-SQL statement that is executed when boolean_expression evaluates to FALSE or NULL.

Transact-SQL syntax conventions

Syntax

IF boolean_expression
    { sql_statement | statement_block }
[ ELSE
    { sql_statement | statement_block } ]

Arguments

boolean_expression

An expression that returns TRUE or FALSE. If the boolean_expression contains a SELECT statement, the SELECT statement must be enclosed in parentheses.

{ sql_statement | statement_block }

Any valid Transact-SQL statement or statement grouping as defined with a statement block. To define a statement block (batch), use the control-of-flow language keywords BEGIN and END. Although all Transact-SQL statements are valid within a BEGIN...END block, certain Transact-SQL statements shouldn't be grouped together within the same batch (statement block).

Return types

Boolean

Examples

The Transact-SQL code samples in this article use the AdventureWorks2022 or AdventureWorksDW2022 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

A. Use a Boolean expression

The following example has a Boolean expression (1 = 1) that is true and, therefore, prints the first statement.

IF 1 = 1 PRINT 'Boolean expression is true.'
ELSE PRINT 'Boolean expression is false.';

The following example has a Boolean expression (1 = 2) that is false, and therefore prints the second statement.

IF 1 = 2 PRINT 'Boolean expression is true.'
ELSE PRINT 'Boolean expression is false.';
GO

B. Use a query as part of a Boolean expression

The following example executes a query as part of the Boolean expression. Because there are 10 bikes in the Product table that meet the condition in the WHERE clause, the first print statement executes. You can change > 5 to > 15, to see how the second part of the statement could execute.

USE AdventureWorks2022;
GO

IF (SELECT COUNT(*)
    FROM Production.Product
    WHERE Name LIKE 'Touring-3000%'
) > 5
    PRINT 'There are more than 5 Touring-3000 bicycles.'
ELSE
    PRINT 'There are 5 or less Touring-3000 bicycles.';
GO

C. Use a statement block

The following example executes a query as part of the Boolean expression and then executes slightly different statement blocks based on the result of the Boolean expression. Each statement block starts with BEGIN and completes with END.

USE AdventureWorks2022;
GO

DECLARE @AvgWeight DECIMAL(8, 2),
    @BikeCount INT

IF (
    SELECT COUNT(*)
    FROM Production.Product
    WHERE Name LIKE 'Touring-3000%'
) > 5
BEGIN
    SET @BikeCount = (
            SELECT COUNT(*)
            FROM Production.Product
            WHERE Name LIKE 'Touring-3000%'
    );
    SET @AvgWeight = (
            SELECT AVG(Weight)
            FROM Production.Product
            WHERE Name LIKE 'Touring-3000%'
    );

    PRINT 'There are ' + CAST(@BikeCount AS VARCHAR(3)) + ' Touring-3000 bikes.'
    PRINT 'The average weight of the top 5 Touring-3000 bikes is ' + CAST(@AvgWeight AS VARCHAR(8)) + '.';
END
ELSE
BEGIN
    SET @AvgWeight = (
            SELECT AVG(Weight)
            FROM Production.Product
            WHERE Name LIKE 'Touring-3000%'
    );

    PRINT 'Average weight of the Touring-3000 bikes is ' + CAST(@AvgWeight AS VARCHAR(8)) + '.';
END;
GO

D. Use nested IF...ELSE statements

The following example shows how an IF...ELSE statement can be nested inside another. Set the @Number variable to 5, 50, and 500, to test each statement.

DECLARE @Number INT;
SET @Number = 50;

IF @Number > 100
    PRINT 'The number is large.';
ELSE
BEGIN
    IF @Number < 10
        PRINT 'The number is small.';
    ELSE
        PRINT 'The number is medium.';
END;
GO

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

E: Using a query as part of a Boolean expression

The following example uses IF...ELSE to determine which of two responses to show the user, based on the weight of an item in the DimProduct table in the AdventureWorksDW2012 database.

DECLARE @maxWeight FLOAT, @productKey INT;

SET @maxWeight = 100.00;
SET @productKey = 424;

IF @maxWeight <= (
    SELECT [Weight]
    FROM DimProduct
    WHERE ProductKey = @productKey;
)
BEGIN
    SELECT @productKey,
        EnglishDescription,
        [Weight],
        'This product is too heavy to ship and is only available for pickup.'
    FROM DimProduct
    WHERE ProductKey = @productKey;
END
ELSE
BEGIN
    SELECT @productKey,
        EnglishDescription,
        [Weight],
        'This product is available for shipping or pickup.'
    FROM DimProduct
    WHERE ProductKey = @productKey;
END

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