{//最简单、原始的、可能的查询计划
public Plan createPlan(QueryData data, Transaction tx)
{
//第一步：为每一个出现的表或者视图定义创建一个plan
List <Plan> plans = new List <Plan>();
foreach (string tblname in data.tables())
{
string viewdef = SimpleDB.mdMgr().getViewDef(tblname, tx);
if (viewdef != null)
{
plans.Add(SimpleDB.planner().createQueryPlan(viewdef, tx));
}
else
{
plans.Add(new TablePlan(tblname, tx));
}
}
//第二步：创建所有表计划的叉积运算
Plan p = plans[0];
plans.RemoveAt(0);
foreach (Plan nextplan in plans)
{
p = new ProductPlan(p, nextplan);
}
//第三步：为predicate添加一个选择运算selection
p = new SelectPlan(p, data.pred());
//第四步：做字段名称上的投影运算
p = new ProjectPlan(p, data.fields());
return(p);
}
//---------------------------------------------------------------------------------------
public IndexInfo(string idxname, string tblname, string fldname, Transaction tx)
{
this.idxname = idxname;
this.fldname = fldname;
this.tx = tx;
ti = SimpleDB.mdMgr().getTableInfo(tblname, tx);
si = SimpleDB.mdMgr().getStatInfo(tblname, ti, tx);
}
public TablePlan(string tblname, Transaction tx)
{//根据指定表在查询树种创建一个叶子节点
this.tx = tx;
ti = SimpleDB.mdMgr().getTableInfo(tblname, tx);
si = SimpleDB.mdMgr().getStatInfo(tblname, ti, tx);
}
public int executeCreateIndex(CreateIndexData data, Transaction tx)
{
SimpleDB.mdMgr().createIndex(data.indexName(), data.tableName(), data.fieldName(), tx);
return(0);
}
public int executeCreateView(CreateViewData data, Transaction tx)
{
SimpleDB.mdMgr().createView(data.viewName(), data.viewDef(), tx);
return(0);
}
public int executeCreateTable(CreateTableData data, Transaction tx)
{
SimpleDB.mdMgr().createTable(data.tableName(), data.newSchema(), tx);
return(0);
}