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# Working with Members, Tuples, and Sets (MDX)

MDX provides numerous functions that return one or more members, tuples, or sets; or that act upon a member, tuple, or set.

## Member Functions

MDX provides several functions for retrieving members from other MDX entities, such as from dimensions, levels, sets, or tuples. For example, the FirstChild function is a function that acts upon a member and returns a member.

To obtain the first child member of the Time dimension, you can explicitly state the member, as in the following example.

```SELECT [Date].[Calendar Year].[CY 2001] on 0

```

You can also use the FirstChild function to return the same member, as in the following example.

```SELECT [Date].[Calendar Year].FirstChild on 0

```

## Tuple Functions

MDX provides several functions that return tuples, and they can be used anywhere that a tuple is accepted. For example, the Item (Tuple) (MDX) function can be used to extract the first tuple from set, which is very useful when you know that a set is composed of a single tuple and you want to supply that tuple to a function that requires a tuple.

The following example returns the first tuple from within the set of tuples on the column axis.

```SELECT {
([Measures].[Reseller Sales Amount]
,[Date].[Calendar Year].[CY 2003]
)
, ([Measures].[Reseller Sales Amount]
,[Date].[Calendar Year].[CY 2004]
)
}.Item(0)
ON COLUMNS
```

## Set Functions

MDX provides several functions that return sets. Explicitly typing tuples and enclosing them in braces is not the only way to retrieve a set. For more information about the members function to return a set, see Key Concepts in MDX (MDX). There are many additional set functions.

The colon operator lets you use the natural order of members to create a set. For example, the set shown in the following example contains tuples for the 1st through the 4th quarter of calendar year 2002.

```SELECT
{[Calendar Quarter].[Q1 CY 2002]:[Calendar Quarter].[Q4 CY 2002]}
ON 0
```

If you do not use the colon operator to create the set, you can create the same set of members by specifying the tuples in the following example.

```SELECT {
[Calendar Quarter].[Q1 CY 2002],
[Calendar Quarter].[Q2 CY 2002],
[Calendar Quarter].[Q3 CY 2002],
[Calendar Quarter].[Q4 CY 2002]
} ON 0

```

The colon operator is an inclusive function. The members on both sides of the colon operator are included in the resulting set.

## Array Functions

An array function acts upon a set and returns an array. For more information about array functions, see MDX Function Reference (MDX).

## Hierarchy Functions

A hierarchy function returns a hierarchy by acting upon a member, level, hierarchy, or string. For more information about hierarchy functions, see MDX Function Reference (MDX).

## Level Functions

A level function returns a level by acting upon a member, level, or string. For more information about level functions, see MDX Function Reference (MDX).

## Logical Functions

A logical function acts upon a MDX expression to return information about the tuples, members, or sets in the expression. For example, the IsEmpty (MDX) function evaluates whether an expression has returned an empty cell value. For more information about logical functions, see MDX Function Reference (MDX).

## Numeric Functions

A numeric function acts upon a MDX expression to return a scalar value. For example, the Aggregate (MDX) function returns a scalar value calculated by aggregating measures over the tuples in a specified set. For more information about numeric functions, see MDX Function Reference (MDX).

## String Functions

A string function acts upon a MDX expression to return a string. For example, the UniqueName (MDX) function returns a string value containing the unique name of a dimension, hierarchy, level, or member. For more information about string functions, see MDX Function Reference (MDX).

#### Reference

MDX Function Reference (MDX)

#### Concepts

Key Concepts in MDX (MDX)

#### Other Resources

MDX Query Fundamentals (MDX)

#### Help and Information

Getting SQL Server 2005 Assistance
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