经常有人说count(1)比count(*)快。实际上是这样吗？不是的，作为数据库的衡量性能的逻辑读来说，是没有差异的。但是在实际的多次反复测试中，我们可以来对比看看真实状况。

SQL>  create table  t as select * from  all_objects;

Table created.

SQL> select count(*) from  all_objects;

  COUNT(*)
----------
      3789

SQL> desc t                   
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 OWNER                                     NOT NULL VARCHAR2(30)
 OBJECT_NAME                               NOT NULL VARCHAR2(30)
 SUBOBJECT_NAME                                     VARCHAR2(30)
 OBJECT_ID                                 NOT NULL NUMBER
 DATA_OBJECT_ID                                     NUMBER
 OBJECT_TYPE                                        VARCHAR2(18)
 CREATED                                   NOT NULL DATE
 LAST_DDL_TIME                             NOT NULL DATE
 TIMESTAMP                                          VARCHAR2(19)
 STATUS                                             VARCHAR2(7)
 TEMPORARY                                          VARCHAR2(1)
 GENERATED                                          VARCHAR2(1)
 SECONDARY                                          VARCHAR2(1)

先 delete statistics , 各方式分别求 1000次 count 
然后 analyze table ,各方式分别求 1000次 count 
然后做个时间对比 
 
服务器无外界干扰的情况下的反复测试的结果如下 
declare 
 n_count number; 
 n_time0 number; 
 n_time1 number; 
 n_time2 number; 
 n_time3 number; 
 n_time4 number; 
 
 begin 
 execute immediate'analyze table t delete statistics'; 
 
 
 select count(*) into n_count from t; 
 
 n_time0 := dbms_utility.get_time; 
 for i in 1..1000 loop 
 select /*+index(t t_index)*/ count(*) into n_count from t; 
 end loop; 
 
 n_time1 := dbms_utility.get_time; 
 for i in 1..1000 loop 
 select count(*) into n_count from t; 
 end loop; 
 
 n_time2 := dbms_utility.get_time; 
 
 for i in 1..1000 loop 
 select count(1) into n_count from t; 
 end loop; 
 n_time3 := dbms_utility.get_time; 
 for i in 1..1000 loop 
 select count(rowid) into n_count from t; 
 end loop; 
 n_time4 := dbms_utility.get_time; 
 
 dbms_output.put_line('the count of the table T : '||to_char(n_count)); 
 dbms_output.put_line('before analyze ,loop 1000,/*+hints*/count(*) :'||to_char(n_time1 - n_time0 )); 
 dbms_output.put_line('before analyze ,loop 1000,count(*) :'||to_char(n_time2 - n_time1)); 
 dbms_output.put_line('before analyze ,loop 1000,count(1) :'||to_char(n_time3 - n_time2)); 
 dbms_output.put_line('before analyze ,loop 1000,count(rowid) :'||to_char(n_time4 - n_time3)); 
 
 execute immediate'analyze table t compute statistics'; 
 
 select count(*) into n_count from t; 
 n_time1 := dbms_utility.get_time; 
 for i in 1..1000 loop 
 select count(*) into n_count from t; 
 end loop; 
 
 n_time2 := dbms_utility.get_time; 
 
 for i in 1..1000 loop 
 select count(1) into n_count from t; 
 end loop; 
 n_time3 := dbms_utility.get_time; 
 for i in 1..1000 loop 
 select count(rowid) into n_count from t; 
 end loop; 
 n_time4 := dbms_utility.get_time; 
 
 dbms_output.put_line('the count of the table T : '||to_char(n_count)); 
 dbms_output.put_line('after analyze ,loop 1000,count(*) :'||to_char(n_time2 - n_time1)); 
 dbms_output.put_line('after analyze ,loop 1000,count(1) :'||to_char(n_time3 - n_time2)); 
 dbms_output.put_line('after analyze ,loop 1000,count(rowid) :'||to_char(n_time4 - n_time3)); 
 
 end; 

the count of the table T : 3789
before analyze ,loop 1000,/*+hints*/count(*) :71
before analyze ,loop 1000,count(*) :63
before analyze ,loop 1000,count(1) :91
before analyze ,loop 1000,count(rowid) :88
the count of the table T : 3789
after analyze ,loop 1000,count(*) :28
after analyze ,loop 1000,count(1) :28
after analyze ,loop 1000,count(rowid) :79

PL/SQL procedure successfully completed.

SQL> /
the count of the table T : 3789
before analyze ,loop 1000,/*+hints*/count(*) :72
before analyze ,loop 1000,count(*) :61
before analyze ,loop 1000,count(1) :88
before analyze ,loop 1000,count(rowid) :85
the count of the table T : 3789
after analyze ,loop 1000,count(*) :28
after analyze ,loop 1000,count(1) :27
after analyze ,loop 1000,count(rowid) :82

PL/SQL procedure successfully completed.

从这里我们可以看出在时间的对比上，同样通过全表扫描和走索引，除了count(rowid)在走索引的时候明显慢外，其他情况下差异都不是很大，很明显，对于这样的求和来说，我们使用 count(*) 是没有什么不好的，count(1)更快纯粹是一个谬论。

更多的讨论可以参考

http://www.cnoug.org/viewthread.php?tid=857&highlight=count%2Bbiti_rainy