{//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);
}
static void doUpdate(string cmd)
{
Planner planner = SimpleDB.planner();
Transaction tx = new Transaction();
int num = planner.executeUpdate(cmd, tx);
tx.commit();
System.Console.WriteLine(num + " records affected");
}
static void doQuery(string cmd)
{
int length;
string format;
Planner planner = SimpleDB.planner();
Transaction tx = new Transaction();
Plan p = planner.createQueryPlan(cmd, tx);
Schema sch = p.schema();
foreach (string fldname in sch.fields())
{
if (sch.type(fldname) == Schema.INTEGER)
{
length = Math.Max(5, fldname.Length) + 2;
format = "{0," + length + "}";
Console.Write(format, fldname);
}
else
{
length = Math.Max(sch.length(fldname), fldname.Length) + 2;
format = "{0," + length + "}";
Console.Write(format, fldname);
}
}
Console.WriteLine();
Scan s = p.open();
while (s.next())
{
foreach (string fldname in sch.fields())
{
if (sch.type(fldname) == Schema.INTEGER)
{
length = Math.Max(5, fldname.Length) + 2;
format = "{0," + length + "}";
Console.Write(format, s.getInt(fldname));
}
else
{
length = Math.Max(sch.length(fldname), fldname.Length) + 2;
format = "{0," + length + "}";
Console.Write(format, s.getString(fldname));
}
}
Console.WriteLine();
}
s.close();
tx.commit();
}