The explain function compiles a SQL statement and returns
      a description of the compilation as a result set. The set consists
      of one column, a varchar, which corresponds to each line of the
      description but may be long, several hundred characters.The output is not a complete disassembly of the query graph but
      is detailed enough to show the join order, subquery structure and the
      order of evaluation of predicates as well as the splitting of a
      distributed VDB query over different data sources.The optional cursor type can be one of the SQL_CURSOR_<xx>
      constants. The default is 0, for forward only. If the statement is a
      SELECT and the cursor type is not forward only, the auxiliary SQL
      statements used by the cursor implementation are shown.