Explain EXPLAIN (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 1)
     Identifier arr
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier index_test
    Function has (children 1)
     ExpressionList (children 2)
      Function arrayMap (children 1)
       ExpressionList (children 2)
        Function lambda (children 1)
         ExpressionList (children 2)
          Function tuple (children 1)
           ExpressionList (children 1)
            Identifier x
          Function lower (children 1)
           ExpressionList (children 1)
            Identifier x
        Identifier arr
      Function lower (children 1)
       ExpressionList (children 1)
        Literal \'a_12\'
    Set
