Filter SUMMARIZECOLUMNS

问题

How to construct filter tables for SUMMARIZECOLUMNS function?

The SUMMARIZECOLUMNS has the following pattern:

SUMMARIZECOLUMNS( 
    ColumnName1, ...
    ColumnNameN,
    FilterTable1,     -- my question concerns this line
    FilterTableN, 
    Name1, [measure1], 
    NameN, [measure2], 
)

I have checked that the following 3 patterns work. They return the same results, at least for the simple sample data I used.

SUMMARIZECOLUMNS (
    T[col],
    FILTER( T, T[col] = "red" ) 
)

SUMMARIZECOLUMNS (
    T[col],
    CALCULATETABLE( T, T[col] = "red" ) 
)

SUMMARIZECOLUMNS (
    T[col],
    CALCULATETABLE ( T, KEEPFILTERS ( T[col] = "red" ) )
)

Is any of these patterns superior over the other?

Reference: https://www.sqlbi.com/articles/introducing-summarizecolumns/

Update

I would be interested in an answer that contains a query plan analysis or link to credible source. I would be grateful if you mentioned using the SUMMARIZECOLUMNS function when grouping columns from multiple tables.

回答1:

You can also construct them the way PowerBI does, using VAR:

VAR  __MyFilterTable = FILTER( T, T[col] = "red" ) 

RETURN
SUMMARIZECOLUMNS (
    T[col],
    __MyFilterTable
)

Which is more efficient will depend on the complexity your filtering, so there is no "one size fits all" rule necessarily. For a simple table level filter, just FILTER will suffice. I caution you that Line 1, where you're filtering the entire table T, is a bad idea. It's much more performant to only filter a single column. When you filter the entire table, DAX materializes the entire table in memory, while the following just materializes the one value of T[col]:

VAR  __MyFilterTable = FILTER( ALL(T[col]), T[col] = "red" ) // This is better.

RETURN
SUMMARIZECOLUMNS (
    T[col],
    __MyFilterTable
)

You can do even better than that, conceptually. You can basically tell DAX, "I know this is a value, so don't even look in the table for it. Just make me a table and treat it as though I filtered it. Like this:

VAR  __MyFilterTable = TREATAS ({"red"}, T[col] )

RETURN
SUMMARIZECOLUMNS (
    T[col],
    __MyFilterTable
)

Again, this is the pattern that PowerBI uses when performing its filters.

BTW, Creating the filter tables a the top vs. creating them inline with SUMMARIZECOLUMNS() won't make any difference for speed. Avoid using CALCULATETABLE() as you've done here generally.

You can also do this as well, though you aren't likely to see a speed increase generally:

CALCULATETABLE(
    SUMMARIZECOLUMNS (
        T[col]
    ),
    KEEPFILTERS(T[col] = "red")
)

来源：https://stackoverflow.com/questions/59931193/filter-summarizecolumns

标签

powerbi

dax