Explain EXPLAIN (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 1)
     Function count (children 1)
      ExpressionList
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       Subquery (children 1)
        SelectWithUnionQuery (children 1)
         ExpressionList (children 1)
          SelectQuery (children 3)
           ExpressionList (children 1)
            Identifier key
           TablesInSelectQuery (children 2)
            TablesInSelectQueryElement (children 1)
             TableExpression (children 1)
              TableIdentifier t1
            TablesInSelectQueryElement (children 2)
             TableExpression (children 1)
              TableIdentifier t2
             TableJoin
           Function greaterOrEquals (children 1)
            ExpressionList (children 2)
             Identifier t1.value
             Function toDateTime (children 1)
              ExpressionList (children 1)
               Function toString (children 1)
                ExpressionList (children 1)
                 Identifier t2.value
    Function equals (children 1)
     ExpressionList (children 2)
      Identifier key
      Literal UInt64_162601
    Set
