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$first = DB::table('user_prod')
->select('user_id', DB::raw("NULL as debit")) //shows 'null' because the 'debit' column does not exist in this table
->where('user_id', '=', Auth::user()->id);
$second = DB::table('user_transaction')
->select('user_id', DB::raw("debit")) //shows the value of the column 'debit' table 'user_transaction'
->where('user_id', '=', Auth::user()->id)
->union($first)
->get();