Question

i have 2 tables(result of two separate SQL queries and this result will be contained by List<Object> where each object represents 1 row of the database )

Table_1

• Dimension_1
• Dimension_2
• Fact_1

Table_2

• Dimension_1
• Dimension_2
• Fact_2

I want to join these two result in the RESULTSET AS

Table_Resultant

• Dimension_1
• Dimension_2
• Fact_1
• Fact_2

Due to some complication in querying part in my system i can’t issue single query for the resultant table, and due to these limitations i will have have to join the two results List <object>(table_1 & table_2) into table_resultant every time

what are the possible approach for the Problem?

Is creating a Temporary table(to join the two resultsets) in MYSQL can be a potential solution???
Yes I am allowed to create temporary tables in Mysql

YES,”COMPLEX” SQL is permitted on the 2 “Results” to GET the resultant_table

Answer 1

So you can do Union but not Join ? Could you clarify if you need to match values of Dimension1 and Dimension2 in the two source tables ? Or if you just need to take all values from both tables and merge them in the resultant one (in which case yes an Union might do the trick)

You need a full outer join, assuming that’s not possible in your query system, here’s the outline of a solution, assuming that:

1. Fact1 and 2 are >=0 ints and 
2. no row in tablex where factx is null.

Select dimension1,dimension2,max(Fact1),max(Fact2) 
From (Select dimension1, dimension2, Fact1, -1 as Fact2 
      UNION 
      Select dimension1, dimension2, -1 , Fact2 ) 
GROUP by dimension1, dimension2 

That’s not the final solution, it will not return NULL for fact1 or 2 when the join doesn’t match. For that of course you’d have to use CASE, or maybe if your querying system thinks that max(NULL,1)=1

Full solution with Union:

Select dimension1, dimension2,  
       CASE WHEN max(Fact1) = -1 THEN NULL ELSE Fact1 END,  
       CASE WHEN max(Fact2) = -1 THEN NULL ELSE Fact2 END,  
From (Select dimension1, dimension2, Fact1, -1 as Fact2  
      UNION 
      Select dimension1, dimension2, -1 , Fact2 )  
GROUP by dimension1, dimension2  

If you can do a FULL OUTER JOIN on the two resultsets then it will look like this

Select isnull(t1.dimension1, t2.dimension1),   
       isnull(t1.dimension2,t2.dimension2),  
       t1.fact1,  
       t2.fact2  
FROM table1 t1 
OUTER JOIN table2 t2   
ON t1.dimension1=t2.dimension1 and t1.dimension2=t2.dimension2