select 查詢列表
from 表
【where 篩選條件】
order by 排序列表 【asc|desc】
select
* from
employees
order by salary desc ;
從低到高是asc（預設是asc）
select
* from
employees
where department_id >= 90
order by hiredate asc ;
select
*,salary * 12 * (1+ ifnull(commission_pct, 0)) as 年薪
from
employees
order by 年薪 desc ;
select
length(last_name) as 位元組長度,
last_name,
salary
from
employees
order by 位元組長度 desc;
select
* from
employees
order by salary asc,
employee_id desc ;
測試題select
last_name,
department_id,
salary * 12 * (1+ ifnull(commission_pct, 0)) as 年薪
from
employees
order by 年薪 desc,
last_name asc ;
select
last_name,
salary
from
employees
where salary not between 8000
and 17000
order by salary desc ;
select
* from
employees
where email like '%e%'
order by length(email) desc,
department_id asc ;
4. 常見函式
呼叫：select 函式名(實參列表) 【from 表】;
特點：分類：
單行函式
select
concat(upper(last_name), lower(first_name)) as 姓名
from
employees ;
select
substr(
'李莫愁愛上了陸展元',
6) as output ;
select
substr(
'李莫愁愛上了陸展元',1,3
) output ;
select
concat(
upper(substr(last_name, 1, 1)),
'_',
lower(substr(last_name, 2))
) as output
from
employees ;
select
instr(
'楊不悔愛上了殷六俠',
'殷六俠'
) as output ;
select
length(trim(' 張翠山 ')) as output ;
select
trim('a' from 'aaa張a翠aa山aaaaa') as output ;
數學函式
日期函式
select
year(hiredate) 年
from
employees ;
select
str_to_date('1998-3-2', '%y-%c-%d') as output ;
select
* from
employees
where hiredate = str_to_date('4-3 1992', '%c-%d %y') ;
select
date_format(now(), '%y年%m月%d日)') as output ;
select
last_name,
date_format(hiredate, '%m月/%d日 %y年') as 入職日期
from
employees
where commission_pct is not null ;
其他函式
select version(); 當前資料庫伺服器的版本
select database(); 當前開啟的資料庫
select user(); 當前使用者
password('字元'); 返回該字元的密碼形式
md5('字元'); 也是加密的一種形式（md5）
select
last_name,
commission_pct,
if(commission_pct is null,
'沒獎金，呵呵',
'有獎金，嘻嘻'
) 備註
from
employees ;
語法：case 要判斷的字段或表示式
when 常量1 then 要顯示的值1或語句1;
when 常量2 then 要顯示的值2或語句2;
...else 要顯示的值n或語句n;
end查詢員工的工資，要求：
部門號=30，顯示的工資為1.1倍
部門號=40，顯示的工資為1.2倍
部門號=50，顯示的工資為1.3倍
其他部門，顯示的工資為原工資
select
salary as 原始工資,
department_id,
case
department_id
when 30
then salary * 1.1
when 40
then salary * 1.2
when 50
then salary * 1.3
else salary
end as 新工資
from
employees ;
case
when 條件1 then 要顯示的值1或語句1
when 條件2 then 要顯示的值2或語句2
...else 要顯示的值n或語句n
end查詢員工的工資情況
如果工資》20000，顯示a級別
如果工資》15000，顯示b級別
如果工資》10000，顯示c級別
否則，顯示d級別
select
salary,
case
when salary > 20000
then 'a'
when salary > 15000
then 'b'
when salary > 10000
then 'c'
else 'd'
end as 工資級別
from
employees ;
測試題
select now();
select
employee_id,
last_name,
salary,
salary * 1.2 as "new salary"
from
employees ;
select
last_name,
length(last_name)
from
employees
order by substr(last_name, 1, 1) ;
select
concat(
last_name,
' earns ',
salary,
' monthly but wants ',
salary * 3
) as "dream salary"
from
employees ;
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_pre'
then 'd'
when 'st_clerk'
then 'e'
end as grade
from
employees
where job_id = 'ad_pres' ;
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