CreateQuery mutation_delete_null_rows (children 3)
 Identifier mutation_delete_null_rows
 Columns definition (children 1)
  ExpressionList (children 3)
   ColumnDeclaration EventDate (children 1)
    DataType Date
   ColumnDeclaration CounterID (children 1)
    DataType Nullable (children 1)
     ExpressionList (children 1)
      DataType String
   ColumnDeclaration UserID (children 1)
    DataType Nullable (children 1)
     ExpressionList (children 1)
      DataType UInt32
 Storage definition (children 2)
  Function MergeTree (children 1)
   ExpressionList
  Identifier EventDate
