這裏寫目錄標題
語言
DQL(data query language)(數據 查詢 語言)
SQL(s=select)(選擇 查詢 語言)
DML(data manipulation language)(數據 操作 語言)
DDL(data define language)(數據定義語言)
TCL(transaction control language)(事務控制語言)
查詢
基礎查詢
select 查詢列表 from 表名;
特點:查詢的結果集 是一個虛擬表(打印內容)
select後面跟的查詢列表,可以有多個部分組成,中間用逗號隔開:select 字段1,字段2,表達式 from 表;
執行順序
① from子句
② select子句
查詢列表可以是:字段、表達式、常量、函數等
USE myemployees;
一、查詢常量
SELECT 100 ;
二、查詢表達式
SELECT 100%3;
三、查詢單個字段
SELECT last_name
FROM employees
;
四、查詢多個字段
SELECT last_name
,email
,employee_id
FROM employees;
五、查詢所有字段
SELECT * FROM employees
;
查詢函數(調用函數,獲取返回值)
SELECT DATABASE();
SELECT VERSION();
SELECT USER();
起別名
方式一:使用as關鍵字
SELECT USER() AS 用戶名;
SELECT USER() AS “用戶名”;
SELECT USER() AS ‘用戶名’;
SELECT last_name AS “姓 名” FROM employees;
方式二:使用空格
SELECT USER() 用戶名;
SELECT USER() “用戶名”;
SELECT USER() ‘用戶名’;
SELECT last_name “姓 名” FROM employees;
mysql> select last_name as 'xing ming' from employees;
+-------------+
| xing ming |
+-------------+
| K_ing |
| Kochhar |
| De Haan |
| Hunold |
+的作用
-需求:查詢 first_name 和last_name 拼接成的全名,最終起別名爲:姓 名
方案1:使用+ pass×
SELECT first_name+last_name AS “姓 名”
FROM employees;
方案2:使用concat拼接函數
SELECT CONCAT(first_name,last_name) AS “姓 名”
FROM employees;
mysql> select concat(first_name,last_name) as 'xing ming' from employees;
+------------------+
| xing ming |
+------------------+
| StevenK_ing |
| NeenaKochhar |
| LexDe Haan |
| AlexanderHunold |
| BruceErnst |
| DavidAustin |
| ValliPataballa |
| DianaLorentz |
| NancyGreenberg |
distinct的使用(去重)
mysql> select department_id from employees; #有重複
+---------------+
| department_id |
+---------------+
| NULL |
| 10 |
| 20 |
| 20 |
| 30 |
| 30 |
| 30 |
| 30 |
| 30 |
| 30 |
distinct adj. 明顯的;獨特的;清楚的;有區別的
查詢員工涉及到的部門編號有哪些
SELECT DISTINCT department_id FROM employees;
mysql> select distinct department_id from employees; #無重複
+---------------+
| department_id |
+---------------+
| NULL |
| 10 |
| 20 |
| 30 |
| 40 |
| 50 |
| 60 |
| 70 |
| 80 |
| 90 |
| 100 |
| 110 |
+---------------+
12 rows in set (0.00 sec)
查看錶的結構
DESC employees;
列 columns
SHOW COLUMNS FROM employees;
條件查詢
select 查詢列表
from 表名
where 篩選條件;
執行順序:
①from子句
②where子句
③select子句
select last_name,first_name from employees where salary>20000;
按關係表達式篩選
關係運算符:> < >= <= = <> (或 != )(不等於)
mysql> select * #要查的東西
-> from employees #表名
-> where department_id <> 100; #條件
+-------------+-------------+-------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| employee_id | first_name | last_name | email | phone_number | job_id | salary | commission_pct | manager_id | department_id | hiredate |
+-------------+-------------+-------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| 100 | Steven | K_ing | SKING | 515.123.4567 | AD_PRES | 24000.00 | NULL | NULL | 90 | 1992-04-03 00:00:00 |
| 101 | Neena | Kochhar | NKOCHHAR | 515.123.4568 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 102 | Lex | De Haan | LDEHAAN | 515.123.4569 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 103 | Alexander | Hunold | AHUNOLD | 590.423.4567 | IT_PROG | 9000.00 | NULL | 102 | 60 | 1992-04-03 00:00:00 |
| 104 | Bruce | Ernst | BERNST | 590.423.4568 | IT_PROG | 6000.00 | NULL | 103 | 60 | 1992-04-03 00:00:00 |
| 105 | David | Austin | DAUSTIN | 590.423.4569 | IT_PROG | 4800.00 | NULL | 103 | 60 | 1998-03-03 00:00:00 |
| 106 | Valli | Pataballa | VPATABAL | 590.423.4560 | IT_PROG | 4800.00 | NULL | 103 | 60 | 1998-03-03 00:00:00 |
| 107 | Diana | Lorentz | DLORENTZ | 590.423.5567 | IT_PROG | 4200.00 | NULL | 103 | 60 | 1998-03-03 00:00:00 |
| 114 | Den | Raphaely | DRAPHEAL | 515.127.4561 | PU_MAN | 11000.00 | NULL | 100 | 30 | 2000-09-09 00:00:00 |
| 115 | Alexander | Khoo | AKHOO | 515.127.4562 | PU_CLERK | 3100.00 | NULL | 114 | 30 | 2000-09-09 00:00:00 |
| 116 | Shelli | Baida | SBAIDA | 515.127.4563 | PU_CLERK | 2900.00 | NULL | 114 | 30 | 2000-09-09 00:00:00 |
| 117 | Sigal | Tobias | STOBIAS | 515.127.4564 | PU_CLERK | 2800.00 | NULL | 114 | 30 | 2000-09-09 00:00:00 |
| 118 | Guy | Himuro | GHIMURO | 515.127.4565 | PU_CLERK | 2600.00 | NULL |
案例2:查詢工資<15000的姓名、工資
mysql> select last_name,salary #要查的東西
-> from employees #表名
-> where salary<15000; #篩選條件
+-------------+----------+
| last_name | salary |
+-------------+----------+
| Hunold | 9000.00 |
| Ernst | 6000.00 |
| Austin | 4800.00 |
按邏輯表達式篩選
邏輯運算符:and or not 也可以使用&& || !
案例:查詢獎金率>0.03 或者 員工編號在60-110之間的員工信息
mysql> select *
-> from employees
-> where commission_pct >0.03 or(employee_id >=60 and employee_id<=110);
+-------------+-------------+------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| employee_id | first_name | last_name | email | phone_number | job_id | salary | commission_pct | manager_id | department_id | hiredate |
+-------------+-------------+------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| 100 | Steven | K_ing | SKING | 515.123.4567 | AD_PRES | 24000.00 | NULL | NULL | 90 | 1992-04-03 00:00:00 |
| 101 | Neena | Kochhar | NKOCHHAR | 515.123.4568 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 102 | Lex | De Haan | LDEHAAN | 515.123.4569 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 103 | Alexander
模糊查詢
like
功能:一般和通配符搭配使用,對字符型數據進行部分匹配查詢
常見的通配符:
_ 任意單個字符
% 任意多個字符,支持0-多個
like/not like
案例1:查詢姓名中包含字符a的員工信息
mysql> select *
-> from employees
-> where last_name like '%a%';
+-------------+-------------+------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| employee_id | first_name | last_name | email | phone_number | job_id | salary | commission_pct | manager_id | department_id | hiredate |
+-------------+-------------+------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| 101 | Neena | Kochhar | NKOCHHAR | 515.123.4568 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 102 | Lex | De Haan | LDEHAAN | 515.123.4569 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 105 | David | Austin | DAUSTIN | 590.423.4569 | IT_PROG | 4800.00 | NULL | 103 |
案例2:查詢姓名中包含第三個字符爲x的員工信息
mysql> select *
-> from employees
-> where last_name like '__x%';
+-------------+------------+-----------+-------+--------------------+--------+---------+----------------+------------+---------------+---------------------+
| employee_id | first_name | last_name | email | phone_number | job_id | salary | commission_pct | manager_id | department_id | hiredate |
+-------------+------------+-----------+-------+--------------------+--------+---------+----------------+------------+---------------+---------------------+
| 170 | Tayler | Fox | TFOX | 011.44.1343.729268 | SA_REP | 9600.00 | 0.20 | 148 | 80 | 2014-03-05 00:00:00 |
+-------------+------------+-----------+-------+--------------------+--------+---------+----------------+------------+---------------+---------------------+
1 row in set (0.00 sec)
案例3:查詢姓名中包含第二個字符爲_的員工信息
mysql> select *
-> from employees
-> where last_name like '_\_%';
+-------------+------------+-----------+-------+--------------------+---------+----------+----------------+------------+---------------+---------------------+
| employee_id | first_name | last_name | email | phone_number | job_id | salary | commission_pct | manager_id | department_id | hiredate |
+-------------+------------+-----------+-------+--------------------+---------+----------+----------------+------------+---------------+---------------------+
| 100 | Steven | K_ing | SKING | 515.123.4567 | AD_PRES | 24000.00 | NULL | NULL | 90 | 1992-04-03 00:00:00 |
| 156 | Janette | K_ing | JKING | 011.44.1345.429268 | SA_REP | 10000.00 | 0.35 | 146 | 80 | 2014-03-05 00:00:00 |
+-------------+------------+-----------+-------+--------------------+---------+----------+----------------+------------+---------------+---------------------+
2 rows in set (0.00 sec)
SELECT *
FROM employees
WHERE last_name LIKE '_$_%' ESCAPE '$'; #將¥定義爲轉義字符
escape
vt. 逃避,避開,避免;被忘掉;被忽視
vi. 逃脫;避開;溜走;
in
查詢某字段的值是否屬於指定的列表之內
a in(常量值1,常量值2,常量值3,…)
a not in(常量值1,常量值2,常量值3,…)
in/not in
案例1:查詢部門編號是30/50/90的員工名、部門編號
#方式1:
SELECT last_name,department_id
FROM employees
WHERE department_id IN(30,50,90);
#方式2:
SELECT last_name,department_id
FROM employees
WHERE department_id = 30
OR department_id = 50
OR department_id = 90;
案例2:查詢工種編號不是SH_CLERK或IT_PROG的員工信息
#方式1:
SELECT *
FROM employees
WHERE job_id NOT IN('SH_CLERK','IT_PROG');
#方式2:
SELECT *
FROM employees
WHERE NOT(job_id ='SH_CLERK'
OR job_id = 'IT_PROG');
mysql> select *
-> from employees
-> where not(job_id ='SH_CLERK'
-> or job_id ='IT_PROG');
+-------------+-------------+-------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| employee_id | first_name | last_name | email | phone_number | job_id | salary | commission_pct | manager_id | department_id | hiredate |
+-------------+-------------+-------------+----------+--------------------+------------+----------+----------------+------------+---------------+---------------------+
| 100 | Steven | K_ing | SKING | 515.123.4567 | AD_PRES | 24000.00 | NULL | NULL | 90 | 1992-04-03 00:00:00 |
| 101 | Neena | Kochhar | NKOCHHAR | 515.123.4568 | AD_VP | 17000.00 | NULL | 100 | 90 | 1992-04-03 00:00:00 |
| 10
between and
判斷某個字段的值是否介於xx之間
between and/not between and
案例1:查詢部門編號是30-90之間的部門編號、員工姓名
#方式1:
SELECT department_id,last_name
FROM employees
WHERE department_id BETWEEN 30 AND 90;
#方式2:
SELECT department_id,last_name
FROM employees
WHERE department_id>=30 AND department_id<=90;
案例2:查詢年薪不是100000-200000之間的員工姓名、工資、年薪
SELECT last_name,salary,salary*12*(1+IFNULL(commission_pct,0)) 年薪
FROM employees
WHERE salary*12*(1+IFNULL(commission_pct,0))<100000 OR salary*12*(1+IFNULL(commission_pct,0))>200000;
SELECT last_name,salary,salary*12*(1+IFNULL(commission_pct,0)) 年薪
FROM employees
WHERE salary*12*(1+IFNULL(commission_pct,0)) NOT BETWEEN 100000 AND 200000;
mysql> SELECT last_name,salary,salary*12*(1+IFNULL(commission_pct,0))
-> from employees
-> WHERE salary*12*(1+IFNULL(commission_pct,0)) NOT BETWEEN 100000 AND 200000;
+-------------+----------+----------------------------------------+
| last_name | salary | salary*12*(1+IFNULL(commission_pct,0)) |
+-------------+----------+----------------------------------------+
| K_ing | 24000.00 | 288000.00 |
| Kochhar | 17000.00 | 204000.00 |
| De Haan | 17000.00 | 204000.00 |
| Ernst | 6000.00 | 72000.00 |
| Austin | 4800.00 | 57600.00 |
is null
案例1:查詢沒有獎金的員工信息
SELECT *
FROM employees
WHERE commission_pct IS NULL;
案例2:查詢有獎金的員工信息
SELECT *
FROM employees
WHERE commission_pct IS NOT NULL;
= 只能判斷普通的內容
IS 只能判斷NULL值
<=> 安全等於,既能判斷普通內容,又能判斷NULL值
SELECT *
FROM employees
WHERE salary <=> 10000;
SELECT *
FROM employees
WHERE commission_pct <=> NULL;