SQL> select count(*) from t; COUNT(*) ---------- 4SQL> select count(1) from t; COUNT(1) ---------- 4SQL> select count(a) from t; COUNT(A) ---------- 3SQL> select * from t; A B ---------- ---------- 1 2 1 2 2 2 SQL>
SQL> select count(1),a from t group by a; COUNT(1) A ---------- ---------- 2 1 1 1 2SQL> select count(*),a from t group by a; COUNT(*) A ---------- ---------- 2 1 1 1 2可能和你的数据有关吧
count(1)就是为了避免null,计算包括null值的数
理论上说count(*)和count(1) 是一个效果,不应该有问题啊
----------
4SQL> select count(1) from t; COUNT(1)
----------
4SQL> select count(a) from t; COUNT(A)
----------
3SQL> select * from t; A B
---------- ----------
1 2
1 2
2 2
SQL>
---------- ----------
2 1
1
1 2SQL> select count(*),a from t group by a; COUNT(*) A
---------- ----------
2 1
1
1 2可能和你的数据有关吧