OceanBase COUNT

COUNT({ * | [ DISTINCT | UNIQUE | ALL ] expr }) [ OVER (analytic_clause) ]

注意 
对于 COUNT 函数，从不返回 NULL，如果指定了 expr，即返回 expr 不为 NULL 的统计个数，如果指定 COUNT(*) 返回所有行的统计数目。使用参数 DISTINCT 、UNIQUE 或 ALL 时需要与 expr 用空格隔开。
如果您指定了 DISTINCT 或 UNIQUE 关键字，则 analytic_clause 中不允许出现 order_by_clause 和 windowing_clause。

CREATE TABLE employees(manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT);
INSERT INTO employees VALUES(300, 'Wei',  '2019-09-11',23600);     
INSERT INTO employees VALUES(200, 'Red', '2019-11-05', 23800);
INSERT INTO employees VALUES(100, 'Part',  '2018-10-01',24000);     
INSERT INTO employees VALUES(200, 'Ross',  '2019-06-11',23500);     
INSERT INTO employees VALUES(200, 'Bell', '2019-05-25', 23000);
INSERT INTO employees VALUES(200, 'Part',  '2018-06-11',24500);    
INSERT INTO employees VALUES(100, 'De Haan', '2018-05-01',11000);      
INSERT INTO employees VALUES(100, 'Errazuriz', '2017-07-21', 1400);
INSERT INTO employees VALUES(100, 'Hartstein', '2019-05-01',14000);     
COMMIT;

SELECT last_name, salary,COUNT(*) OVER (ORDER BY salary RANGE BETWEEN 50 PRECEDING 
AND 150 FOLLOWING) AS mov_count FROM employees ORDER BY salary, last_name;

+-----------+--------+-----------+
| LAST_NAME | SALARY | MOV_COUNT |
+-----------+--------+-----------+
| Errazuriz |   1400 |         1 |
| De Haan   |  11000 |         1 |
| Hartstein |  14000 |         1 |
| Bell      |  23000 |         1 |
| Ross      |  23500 |         2 |
| Wei       |  23600 |         1 |
| Red       |  23800 |         1 |
| Part      |  24000 |         1 |
| Part      |  24500 |         1 |
+-----------+--------+-----------+

CREATE TABLE a (
b INT
);
INSERT INTO a VALUES (1);
INSERT INTO a VALUES (null);
INSERT INTO a VALUES (null);
INSERT INTO a VALUES (1);
INSERT INTO a VALUES (null);
INSERT INTO a VALUES (1);
INSERT INTO a VALUES (1);

SELECT COUNT(b) FROM a;

+----------+
| COUNT(B) |
+----------+
|        4 |
+----------+

SELECT COUNT(*) FROM a;

+----------+
| COUNT(*) |
+----------+
|        7 |
+----------+