单行函数案例讲解
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1.显示系统时间(注:日期+时间)
SELECT NOW();
2.查询员工号,姓名,工资,以及工资提高20%后的结果(new salary)
SELECT employee_id,last_name,salary,salary*1.2 "new salary"
FROM employees;
3.将员工的姓名按首字母排序,并写出姓名的长度(length)
SELECT LENGTH(last_name) 长度,SUBSTR(last_name,1,1) 首字符,last_name
FROM employees
ORDER BY 首字符;
4.做一个查询,产生下面的结果
<last_name> earns
Dream Salary
King earns 24000 monthly but wants 72000
SELECT CONCAT(last_name,' earns ',salary,' monthly but wants ',salary*3) AS "Dream Salary"
FROM employees
WHERE salary=24000;
5.使用case-when,按照下面的条件:
job grade
AD_PRES A
ST_MAN B
IT_PROG C
SA_REP D
ST_CLERK E
产生下面的结果
Last_name Job_id Grade
king AD_PRES A
SELECT last_name,job_id AS job,
CASE job_id
WHEN 'AD_PRES' THEN 'A'
WHEN 'ST_MAN' THEN 'B'
WHEN 'IT_PROG' THEN 'C'
WHEN 'SA_REP' THEN 'D'
WHEN 'ST_CLERK' THEN 'E'
END AS GRADE
FROM employeeS
WHERE job_id = 'AD_PRES';