Forum Discussion
left outer join using dax, Multiple to Multiple
I have two tables in my data model, currently, i am exporting them to Excel do the merge there using PQ and import back to PowerBI Data model, as you would imagine, this is not efficient.
i have read about the new " naturalleftoutjoin ", i can't make it to works, if I add the common id, it complains that there is a duplicate columns, if i remove it, it say there is no common column, clearly i don't understand how it works.
so here is my scenario; notice the id is duplicated in both tables and it is by design, so any idea how to create the calculated table Result using DAX ?
Just playing around with CROSSJOIN and UNION as well and maybe a GENERATE using the nonexisting and ROW to provide space for the BLANK value :-) but now I have to take some sleep
Using DAX you can do something like this, but M is probably preferable.
Result = GENERATEALL ( 'Table 1', VAR Table1ID = 'Table 1'[id] RETURN SELECTCOLUMNS ( CALCULATETABLE ( 'Table 2', 'Table 2'[id] = Table1ID ), "price", 'Table 2'[price] ) )Something like this should work. I tested it in a dummy model with physical tables Transformed_TAR, Tostr and 'Table 2' and it worked for me.
Note that I've left you VAR Table1... unchanged except that I've been pedantic and qualified all your column names from Transformed_TAR and Tostr with their table names, e.g. [tag] becomes Transformed_Tar[tag] :
Result = VAR Table1 = UNION ( SELECTCOLUMNS ( FILTER ( Transformed_TAR, Transformed_TAR[current] = "yes" && Transformed_TAR[rem_qty] <> 0 && Transformed_TAR[project phase] = "cons" && Transformed_TAR[P6 ACTIVITY ID] <> BLANK () ), "tag", Transformed_TAR[tag], "id", Transformed_TAR[P6 ACTIVITY ID], "subscan", Transformed_TAR[subscan], "subsystem", Transformed_TAR[TOSTR_Subsystem], "area", Transformed_TAR[Transformed Area], "weight", Transformed_TAR[weight], "drawing", Transformed_TAR[drawing], "phase", Transformed_TAR[project phase], "CREW", Transformed_TAR[crew], "Module", Transformed_TAR[Module], "rem_qty", Transformed_TAR[rem_qty] ), SELECTCOLUMNS ( FILTER ( Tostr, Tostr[remaining_ITR] <> 0 && Tostr[P6 activity id] <> BLANK () ), "tag", Tostr[tag], "id", Tostr[P6 activity id], "subscan", Tostr[subscan], "subsystem", Tostr[SUBSYSTEM], "area", Tostr[Area], "weight", Tostr[weight], "drawing", Tostr[SHEET], "phase", Tostr[Phase], "CREW", Tostr[crew], "Module", Tostr[Module], "rem_qty", Tostr[remaining_ITR] ) ) RETURN GENERATEALL ( Table1, VAR Table1ID = [id] RETURN SELECTCOLUMNS ( CALCULATETABLE ( 'Table 2', 'Table 2'[id] = Table1ID ), "price", 'Table 2'[price] ) )
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Using DAX you can do something like this, but M is probably preferable.
Result = GENERATEALL ( 'Table 1', VAR Table1ID = 'Table 1'[id] RETURN SELECTCOLUMNS ( CALCULATETABLE ( 'Table 2', 'Table 2'[id] = Table1ID ), "price", 'Table 2'[price] ) )Hi mim
Quoting from The Definitive Guide to DAX:
"you might consider the GENERATE function similar to the CROSS APPLY condition in SQL, whereas GENERATEALL is similar to OUTER APPLY in SQL".
GENERATE/GENERATEALL iterate over the rows of first table specified and determine the second table in the context of each row, with freedom as to how the condition relates to that row context.
Performance-wise, I would imagine they perform better than a FILTER(CROSSJOIN()) pattern when the join results in a small subset of the rows of the CROSSJOIN of the two tables.
I haven't really played with NATURALLEFTOUTERJOIN or NATURALINNERJOIN, but I note they require join columns to have the same lineage.
Owen :)
Thx OwenAuger, that helped me a lot !
Hey,
this is odd, I created the screenshot from this
recreating your sample data, a table merge using left outer creates this result
Really wondering whats going on
I need to do it in DAX using calculated table, not PowerQuery, the reason is table 1 and table 2 are already loaded in the Data model using some heavy PowerQery Transformation, which take nearly 20 minutes,
ideally if PQ supported loading table from existing data model, it would have been great, but that's not the case now, I thought it can be possible using DAX.
Silly me, sorry for bothering ...
The DAX functions NATURALLEFTOUTERJOIN() requires an relationship between the tables (one to many), seems a little strange, but thats how the function currently works.
And you can't create a relationship in dax because none of the two columns is unique.
