CreateQuery t (children 3)
 Identifier t
 Columns definition (children 1)
  ExpressionList (children 2)
   ColumnDeclaration a (children 1)
    DataType Nullable (children 1)
     ExpressionList (children 1)
      DataType Int
   ColumnDeclaration b (children 1)
    DataType LowCardinality (children 1)
     ExpressionList (children 1)
      DataType Nullable (children 1)
       ExpressionList (children 1)
        DataType String
 Storage definition (children 3)
  Function MergeTree (children 1)
   ExpressionList
  Function tuple (children 1)
   ExpressionList
  Set
