---
title: "Union  (MDX) | Microsoft Docs"
ms.date: 06/04/2018
ms.prod: sql
ms.technology: analysis-services
ms.custom: mdx
ms.topic: reference
ms.author: owend
ms.reviewer: owend
author: minewiskan
---
# Union  (MDX)


  Returns a set that is generated by the union of two sets, optionally retaining duplicate members.  
  
## Syntax  
  
```  
  
Standard syntax  
Union(Set_Expression1, Set_Expression2 [,...n][, ALL])  
  
Alternate syntax 1  
Set_Expression1 + Set_Expression2 [+...n]  
  
Alternate syntax 2  
{Set_Expression1 , Set_Expression2 [,...n]}  
```  
  
## Arguments  
 *Set Expression 1*  
 A valid Multidimensional Expressions (MDX) expression that returns a set.  
  
 *Set Expression 2*  
 A valid Multidimensional Expressions (MDX) expression that returns a set.  
  
## Remarks  
 This function returns the union of two or more specified sets. With the standard syntax and with alternate syntax 1, duplicates are eliminated by default. With the standard syntax, using the **ALL** flag keeps duplicates in the joined set. Duplicates are deleted from the tail of the set. With alternate syntax 2, duplicates are always retained.  
  
## Examples  
 The following examples demonstrate the behavior of the **Union** function using each syntax.  
  
### Standard syntax, duplicates eliminated  
  
```  
SELECT Union   
   ([Date].[Calendar Year].children  
   , {[Date].[Calendar Year].[CY 2002]}  
   , {[Date].[Calendar Year].[CY 2003]}  
   ) ON 0  
FROM [Adventure Works]  
  
```  
  
### Standard syntax, duplicates retained  
  
```  
SELECT Union   
   ([Date].[Calendar Year].children  
   , {[Date].[Calendar Year].[CY 2002]}  
   , {[Date].[Calendar Year].[CY 2003]}  
   , ALL  
   ) ON 0  
FROM [Adventure Works]  
  
```  
  
### Alternate syntax 1, duplicates eliminated  
  
```  
SELECT   
   [Date].[Calendar Year].children   
   + {[Date].[Calendar Year].[CY 2002]}   
   + {[Date].[Calendar Year].[CY 2003]} ON 0  
FROM [Adventure Works]  
  
```  
  
### Alternate syntax 2, duplicates retained  
  
```  
SELECT   
   {[Date].[Calendar Year].children  
   , [Date].[Calendar Year].[CY 2002]  
   , [Date].[Calendar Year].[CY 2003]} ON 0  
FROM [Adventure Works]  
  
```  
  
## See Also  
 [+ (Union) (MDX)](../mdx/union-mdx-operator-reference.md)   
 [MDX Function Reference (MDX)](../mdx/mdx-function-reference-mdx.md)