<< Click to Display Table of Contents >> ETL > 12.6 > Implementation Guide > Tutorial and implementation guide > Steps > Joining  Column selection

If nothing else is provided, all columns from all joined tables will be present in the output table. It is possible to limit this by providing a white list of columns to be written. Any columns not mentioned in the list will be omitted from the target result (note: key columns are automatically included). To define the required columns, use the following syntax:

 

{

    "id": 1,

    "type": "join",

    "name": "join demo",

    "sources": ["Table1", "Table2", "Table3"],

    "columns": ["Name", "Surname", "Age"],

    "on": ["Computer"],

    "strategy": "outer",

    "target": "joined_os_outer_coalesce"

}