Children returns the set of members one level below a named parent.
{Product.[Demand Loan].Children}

FirstChild returns the… first child one level below a named parent.
{[Product].[Customer Lending].FirstChild}
Returns “Call Participation Purchased”.

The FILTER function is used to filter the dimension based on some kind of data values rather than just the members and their hierarchy on their own. This data might be cube data (numeric or string) or attribute data. This requires a change of thinking from straightforward single dimensions (lists with a hierarchy and occasionally some attributes) to a multi-dimensional space, where every dimension in these cubes must be considered and dealt with.

A classic Top 10 command:
{ TOPCOUNT( {TM1FILTERBYLEVEL( {TM1SUBSETALL( [Product] )}, 0)}, 10, [Test].([Posting Measures].[Amount]) )}
By omitting a sort order it sorts in the default order (which has the values descending in value and breaks any hierarchies present).

TM1Sort is the equivalent of pressing one of the two Sort Ascending or Sort Descending buttons in the subset editor – i.e. sort alphabetically.

TM1SortIndex is the equivalent of pressing one of the two Sort by index, ascending or Sort by index, descending buttons in the subset editor – i.e. sort by the dimension index (dimix).

Order is a standard MDX function that uses a data value from a cube to perform the sort. For example, sort the list of customers according to the sales, or a list of employees according to their length of service.

Selecting members based on their level in the dimension hierarchy (TM1FilterByLevel) or by a pattern of strings in their name (TM1FilterByPattern) can be seen easily by using the Record Expression feature in the subset editor.

The basis for many queries, this returns (almost, see below) the entire dimension, which is the equivalent of clicking the ‘All’ button in the Subset Editor.
TM1SUBSETALL( [Product] )

Note that only the final instance in the first hierarchy of members that are consolidated multiple times is returned.

The Members function, on the other hand, delivers the full dimension, duplicates included:
[Product].Members

In this document many examples of dynamic queries will be given. They all work (exactly as written, just copy-and-paste them into the Expression Window in the Subset Editor of the appropriate dimension to use them) on the simple set of cubes and dimensions shown below. The model is deliberately simple with no special characteristics so you should find it easy to transfer the work to your own model.

TM1 only supports a certain number of functions from the complete MDX specification. Different versions of TM1 will support different functions (and potentially support the in different ways). The valid set of functions for the version of TM1 that you are using can be found in the main Help file, under Reference Material / MDX Function Support. Before trying to write a new query, make sure it is supported, and although some unlisted functions certainly do work they must be used at your own risk.

A static subset is one which never varies in its content.
This query will return the same 3 members (Discount Loan, Term Loan and Retail) every time.
{ [Product].[Discount Loan], [Product].[Term Loan], [Product].[Retail] }

Don’t worry, it gets more exciting from here.

The same basic steps can be followed with all the examples in this document. Generally the examples can be copy-and-pasted into the Expression Window of the Subset Editor of the dimension in question – often Product. Note that it is irrelevant which cube the dimension is being used by; you will get same results whether you open the dimension Subset Editor from within a cube view, the cube tree in Server Explorer or the dimension tree in Server Explorer.