SQL COUNT：示例 - SQL 教程

示例
示例数据库

#1

SELECT COUNT(*) FROM employees;

#2

SELECT COUNT(*) FROM employees WHERE department_id = 6;

#3

SELECT COUNT(*) FROM employees WHERE job_id = 9;

#4

SELECT department_id, COUNT(*) FROM employees GROUP BY department_id;

#5

SELECT e.department_id, department_name, COUNT(*) FROM employees e INNER JOIN departments d ON d.department_id = e.department_id GROUP BY e.department_id;

#6

SELECT e.department_id, department_name, COUNT(*) FROM employees e INNER JOIN departments d ON d.department_id = e.department_id GROUP BY e.department_id ORDER BY COUNT(*) DESC;

#7

SELECT e.department_id, department_name, COUNT(*) FROM employees e INNER JOIN departments d ON d.department_id = e.department_id GROUP BY e.department_id HAVING COUNT(*) > 5 ORDER BY COUNT(*) DESC;

#8

SELECT COUNT(job_id) FROM employees;

#9

SELECT COUNT(DISTINCT manager_id) FROM employees;

表格列表

国家

SELECT * FROM countries;

部门

SELECT * FROM departments;

受抚养人

SELECT * FROM dependents;

员工

SELECT * FROM employees;

工作

SELECT * FROM jobs;

地方

SELECT * FROM locations;

地区

SELECT * FROM regions;

SQL 查询

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结果