UNION and UNION ALL in Looker

Looker Tips & Resources Technical Tips & Tricks
1

You can execute a SQL UNION or UNION ALL operator in both SQL-based derived tables (DT) and persistent derived tables (PDT). The UNION and UNION ALL operators combine the result sets of two queries.

This example shows what a SQL-based DT looks like with a UNION in LookML:

view: union_example {    
  derived_table: {       
    sql: 
       SELECT 1 AS my_int      
       FROM union_example1 
       UNION       
       SELECT 2 AS my_int 
       FROM union_example2 ;;      
   }
}

This results in a derived table that combines the results of both queries.

The difference between UNION and UNION ALL is that UNION ALL does not remove duplicate rows. There are performance considerations to keep in mind when using UNION vs. UNION ALL, because the database server must do additional work to remove the duplicate rows. However, you usually do not want the duplicates.

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