oracle中可用count,Oracle / PLSQL COUNT函数
这个Oracle教程解释了如何使用Oracle / PLSQL COUNT函数。
Count 函数对一组行进行操作并返回一行输出。
您可以使用count具有任何有效表达式的函数。例如，您可以使用COUNT()数字，字符串和数据时间的函数。
空值由count函数忽略。
您可以使用DISTINCT关键字排除重复条目。
语法
Oracle / PLSQL COUNT函数的语法是：
SELECT COUNT( expression )
FROM tables
WHERE conditions;
表达式可以是字段或公式。
实例
CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
ENAME VARCHAR2(10),
JOB VARCHAR2(9),
SAL NUMBER(7, 2),
DEPTNO NUMBER(2));
INSERT INTO EMP VALUES (1, 'SMITH', 'CLERK', 800, 20);
INSERT INTO EMP VALUES (2, 'ALLEN', 'SALESMAN', 1600, 30);
INSERT INTO EMP VALUES (3, 'WARD', 'SALESMAN', 1250, 30);
INSERT INTO EMP VALUES (4, 'JONES', 'MANAGER', 2975, 20);
INSERT INTO EMP VALUES (5, 'MARTIN','SALESMAN', 1250, 30);
INSERT INTO EMP VALUES (6, 'BLAKE', 'MANAGER', 2850, 30);
INSERT INTO EMP VALUES (7, 'CLARK', 'MANAGER', 2850, 10);
INSERT INTO EMP VALUES (8, 'SCOTT', 'ANALYST', 3000, 20);
INSERT INTO EMP VALUES (9, 'KING', 'PRESIDENT',3000, 10);
INSERT INTO EMP VALUES (10,'TURNER','SALESMAN', 1500, 30);
INSERT INTO EMP VALUES (11,'ADAMS', 'CLERK', 1500, 20);
SQL>
SQL> select count(empno) from emp;
COUNT(EMPNO)
------------
11
SQL>
ROWID with Count
使用ROWID计算总行数
SQL>
SQL> select count(rowid) from emp;
COUNT(ROWID)
------------
11
SQL>
count与group by一起使用
Count函数配合group by一起使用实例：
SQL>
SQL> select count(rowid) from emp group by deptno;
COUNT(ROWID)
------------
5
4
2
SQL>
count配合DISTINCT和ALL使用
CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
ENAME VARCHAR2(10),
JOB VARCHAR2(9),
SAL NUMBER(7, 2),
DEPTNO NUMBER(2));
INSERT INTO EMP VALUES (1, NULL, 'CLERK', 800, 20);
INSERT INTO EMP VALUES (2, NULL, 'SALESMAN', 1600, 30);
INSERT INTO EMP VALUES (3, 'WARD', 'SALESMAN', 1250, 30);
INSERT INTO EMP VALUES (4, 'WARD', 'MANAGER', 2975, 20);
INSERT INTO EMP VALUES (5, 'MARTIN','SALESMAN', 1250, 30);
INSERT INTO EMP VALUES (6, 'BLAKE', 'MANAGER', 2850, 30);
INSERT INTO EMP VALUES (7, 'CLARK', 'MANAGER', 2850, 10);
INSERT INTO EMP VALUES (8, 'SCOTT', 'ANALYST', 3000, 20);
INSERT INTO EMP VALUES (9, 'KING', 'PRESIDENT',3000, 10);
INSERT INTO EMP VALUES (10,'TURNER','SALESMAN', 1500, 30);
INSERT INTO EMP VALUES (11,'ADAMS', 'CLERK', 1500, 20);
SQL> select count(ename), count(distinct ename), count(all ename) from emp;
COUNT(ENAME) COUNT(DISTINCTENAME) COUNT(ALLENAME)
------------ -------------------- ---------------
9 8 9
SQL>