如何对此查询使用Oracle组函数计数和group by子句

Question

Create a query to display the total number of employees and, of that total, the number of
employees hired in 1995, 1996, 1997, and 1998. Create appropriate column headings.

假设员工表有以下字段

1. emp_id number

2. firstname varchar

3. hire_date date 等

Answer 1

这可能会有所帮助！根据您的需要更换年份

   SELECT COUNT(*) "Total",
  SUM(DECODE(hire_date,'2010',1,0)) "2010 Count" ,
  SUM(DECODE(hire_date,'2015',1,0)) "2015 Count",
  SUM(DECODE(hire_date,'2014',1,0)) "2014 Count"
FROM emp;