C++ ExpGenerator::generateSamplingExpr方法代码示例

short
PhysSample::codeGen(Generator *generator) 
{  
  // Get a local handle on some of the generator objects.
  //
  CollHeap *wHeap = generator->wHeap();
  Space *space = generator->getSpace();
  MapTable *mapTable = generator->getMapTable();
  ExpGenerator *expGen = generator->getExpGenerator();

  // Allocate a new map table for this node. This must be done
  // before generating the code for my child so that this local
  // map table will be sandwiched between the map tables already
  // generated and the map tables generated by my offspring.
  //
  // Only the items available as output from this node will
  // be put in the local map table. Before exiting this function, all of
  // my offsprings map tables will be removed. Thus, none of the outputs 
  // from nodes below this node will be visible to nodes above it except 
  // those placed in the local map table and those that already exist in
  // my ancestors map tables. This is the standard mechanism used in the
  // generator for managing the access to item expressions.
  //
  MapTable *localMapTable = generator->appendAtEnd();

  // Since this operation doesn't modify the row on the way down the tree,
  // go ahead and generate the child subtree. Capture the given composite row
  // descriptor and the child's returned TDB and composite row descriptor.
  //
  ex_cri_desc * givenCriDesc = generator->getCriDesc(Generator::DOWN);
  child(0)->codeGen(generator);
  ComTdb *childTdb = (ComTdb*)generator->getGenObj();
  ex_cri_desc * childCriDesc = generator->getCriDesc(Generator::UP);
  ExplainTuple *childExplainTuple = generator->getExplainTuple();

  // Geneate the sampling expression.
  //
  ex_expr *balExpr = NULL;
  Int32 returnFactorOffset = 0;
  ValueId val;
  val = balanceExpr().init();
  if(balanceExpr().next(val))
    expGen->generateSamplingExpr(val, &balExpr, returnFactorOffset);

  // Alias the sampleColumns() so that they reference the underlying
  // expressions directly. This is done to avoid having to generate and
  // execute a project expression that simply moves the columns from
  // one tupp to another to reflect the application of the sampledCol
  // function.
  //
//   ValueId valId;
//   for(valId = sampledColumns().init();
//       sampledColumns().next(valId);
//       sampledColumns().advance(valId))
//     {
//       MapInfo *mapInfoChild = localMapTable->getMapInfoAsIs
// 	(valId.getItemExpr()->child(0)->castToItemExpr()->getValueId());
//       GenAssert(mapInfoChild, "Sample::codeGen -- no child map info.");
//       Attributes *attr = mapInfoChild->getAttr();
//       MapInfo *mapInfo = localMapTable->addMapInfoToThis(valId, attr);
//       mapInfo->codeGenerated();
//     }
// check if any of the columns inthe sampled columns are lob columns. If so, return an error.
  ValueId valId;
  for(valId = sampledColumns().init();
      sampledColumns().next(valId);
      sampledColumns().advance(valId))
    {
      const NAType &colType = valId.getType();
      if ((colType.getFSDatatype() == REC_BLOB) ||
	  (colType.getFSDatatype() == REC_CLOB))
	{
	   *CmpCommon::diags() << DgSqlCode(-4322);
	   GenExit();
	}
    }
  // Now, remove all attributes from the map table except the 
  // the stuff in the local map table -- the result of this node.
  //
//  localMapTable->removeAll();

  // Generate the expression to evaluate predicate on the sampled row.
  //
  ex_expr *postPred = 0;
  if (!selectionPred().isEmpty()) {
    ItemExpr * newPredTree 
      = selectionPred().rebuildExprTree(ITM_AND,TRUE,TRUE);

    expGen->generateExpr(newPredTree->getValueId(), ex_expr::exp_SCAN_PRED,
			 &postPred);
  }

  // Construct the Sample TDB.
  //
  ComTdbSample *sampleTdb
    = new(space) ComTdbSample(NULL,
			      balExpr,
			      returnFactorOffset,
			      postPred,
			      childTdb,
//.........这里部分代码省略.........