聚类索引要不要加 order by

数据库要不要加order by给大家两个例子一看就知道了

[sql] view plaincopy
CREATE TABLE Beatles  
  
     (LastName varchar(20) NOT NULL PRIMARY KEY CLUSTERED,  
  
      FirstName varchar(20) NOT NULL UNIQUE NONCLUSTERED);  
  
INSERT INTO Beatles (LastName, FirstName)  
  
SELECT 'Lennon', 'John'  
  
UNION ALL  
  
SELECT 'McCartney', 'Paul'  
  
UNION ALL  
  
SELECT 'Harrison', 'George'  
  
UNION ALL  
  
SELECT 'Starr', 'Ringo';  
  
SELECT LastName FROM Beatles;  
  
DROP TABLE Beatles;  
  
go  
  
   
  
LastName  
  
--------------------  
  
Harrison  
  
Lennon  
  
McCartney  
Starr  
[sql] view plaincopy
CREATE TABLE Stones  
  
     (LastName varchar(20) NOT NULL PRIMARY KEY CLUSTERED,  
  
      FirstName varchar(20) NOT NULL UNIQUE NONCLUSTERED);  
  
INSERT INTO Stones (LastName, FirstName)  
  
SELECT 'Jagger', 'Mick'  
  
UNION ALL  
  
SELECT 'Jones', 'Brian'  
  
UNION ALL  
  
SELECT 'Richards', 'Keith'  
  
UNION ALL  
  
SELECT 'Watts', 'Charlie'  
  
UNION ALL  
  
SELECT 'Wyman', 'Bill';  
  
SELECT LastName FROM Stones;  
  
DROP TABLE Stones;  
  
go  
  
   
  
LastName  
  
--------------------  
  
Wyman  
  
Jones  
  
Watts  
  
Richards  
  
Jagger  

 第一个表没有问题，输出即使没加 order by 也能按照正常输出，但是第二个表却是乱序，为什么那？ 

 

答案就在这个执行计划里，所以，无论何时不要忽略优化器的选择，要不然诡异的现象就会时有发生，另外你都已经有了聚类索引，多加一个order by会死人啊？效率会低啊？我说我自己。