public int executeDelete(DeleteData data, Transaction tx)
{
Plan p = new TablePlan(data.tableName(), tx);
p = new SelectPlan(p, data.pred());
UpdateScan us = (UpdateScan)p.open();
int count = 0;
while (us.next())
{
us.delete();
count++;
}
us.close();
return(count);
}
public int executeModify(ModifyData data, Transaction tx)
{
Plan p = new TablePlan(data.tableName(), tx);
p = new SelectPlan(p, data.pred());
UpdateScan us = (UpdateScan)p.open();
int count = 0;
while (us.next())
{
Constant val = data.newValue().evaluate(us); //返回此处的表达式的常量值
us.setVal(data.targetField(), val); //设置要更改字段处的值
count++;
}
us.close();
return(count);
}