MySQL實現單表查詢的簡單方法

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首先我們來創建表、插入數據：

# 創建表
mysql> create table company.employee5(
    id int primary key AUTO_INCREMENT not null,
    name varchar(30) not null,
    sex enum('male','female') default 'male' not null,
    hire_date date not null,
    post varchar(50) not null,
    job_description varchar(100),
    salary double(15,2) not null,
    office int,
    dep_id int
    );

# 插入數據
mysql> insert into company.employee5(name,sex,hire_date,post,job_description,salary,office,dep_id) values 
    ('jack','male','20180202','instructor','teach',5000,501,100),
    ('tom','male','20180203','instructor','teach',5500,501,100),
    ('robin','male','20180202','instructor','teach',8000,501,100),
    ('alice','female','20180202','instructor','teach',7200,501,100),
    ('tianyun','male','20180202','hr','hrcc',600,502,101),
    ('harry','male','20180202','hr',NULL,6000,502,101),
    ('emma','female','20180206','sale','salecc',20000,503,102),
    ('christine','female','20180205','sale','salecc',2200,503,102),
    ('zhuzhu','male','20180205','sale',NULL,2200,503,102),
    ('gougou','male','20180205','sale','',2200,503,102);

# 查看表結構
mysql> desc employee5;
 
+-----------------+-----------------------+------+-----+---------+----------------+
| Field           | Type                  | Null | Key | Default | Extra          |
+-----------------+-----------------------+------+-----+---------+----------------+
| id              | int(11)               | NO   | PRI | NULL    | auto_increment |
| name            | varchar(30)           | NO   |     | NULL    |                |
| sex             | enum('male','female') | NO   |     | male    |                |
| hire_date       | date                  | NO   |     | NULL    |                |
| post            | varchar(50)           | NO   |     | NULL    |                |
| job_description | varchar(100)          | YES  |     | NULL    |                |
| salary          | double(15,2)          | NO   |     | NULL    |                |
| office          | int(11)               | YES  |     | NULL    |                |
| dep_id          | int(11)               | YES  |     | NULL    |                |
+-----------------+-----------------------+------+-----+---------+----------------+

查詢語法

SELECT 字段1,字段2... FROM 表名
                  WHERE 條件
                  GROUP BY field
                  HAVING 篩選
                  ORDER BY field
                  LIMIT 限制條數；

查看表中所有數據

mysql> select * from employee5;
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
| id | name      | sex    | hire_date  | post       | job_description | salary   | office | dep_id |
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
|  1 | jack      | male   | 2018-02-02 | instructor | teach           |  5000.00 |    501 |    100 |
|  2 | tom       | male   | 2018-02-03 | instructor | teach           |  5500.00 |    501 |    100 |
|  3 | robin     | male   | 2018-02-02 | instructor | teach           |  8000.00 |    501 |    100 |
|  4 | alice     | female | 2018-02-02 | instructor | teach           |  7200.00 |    501 |    100 |
|  5 | tianyun   | male   | 2018-02-02 | hr         | hrcc            |   600.00 |    502 |    101 |
|  6 | harry     | male   | 2018-02-02 | hr         | NULL            |  6000.00 |    502 |    101 |
|  7 | emma      | female | 2018-02-06 | sale       | salecc          | 20000.00 |    503 |    102 |
|  8 | christine | female | 2018-02-05 | sale       | salecc          |  2200.00 |    503 |    102 |
|  9 | zhuzhu    | male   | 2018-02-05 | sale       | NULL            |  2200.00 |    503 |    102 |
| 10 | gougou    | male   | 2018-02-05 | sale       |                 |  2200.00 |    503 |    102 |
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
10 rows in set (0.00 sec)

簡單查詢

簡單查詢

mysql> SELECT * FROM employee5;

mysql> SELECT name, salary, dep_id FROM employee5;

去重DISTINCT

mysql> SELECT post FROM employee5;

mysql> SELECT DISTINCT post  FROM employee5;

注：不能部分使用DISTINCT，通常僅用于某一字段。

通過四則運算查詢

mysql> SELECT name, salary, salary*14 FROM employee5;

mysql> SELECT name, salary, salary*14 AS Annual_salary FROM employee5;

mysql> SELECT name, salary, salary*14 Annual_salary FROM employee5;

定義顯示格式

CONCAT() 函數用于連接字符串

mysql> SELECT CONCAT(name, ' annual salary: ', salary*14)  AS Annual_salary FROM employee5;

條件查詢

a、語法
    select * from 表名 where 條件
b、比較運算符
    大于    小于    大于等于    小于等于    不等于    >        <        >=            <=            
    !=或<>
c、邏輯運算符
    并且    或者    非    and        or        notd、模糊查詢
    like    %           表示任意多個任意字符
    _           表示一個任意字符

e、范圍查詢    in                  表示在一個非連續的范圍內
    between...and...    表示在一個連續的范圍內

f、空判斷
    判斷空：is null
    判斷非空：is not null 

g、優先級
    小括號,not 比較運算符， 邏輯運算符
    and比or優先級高，如果同時出現并希望先選or，需要結合()來使用

單條件查詢

mysql> SELECT name,post FROM employee5 WHERE post='hr';

多條件查詢

mysql> SELECT name,salary FROM employee5 WHERE post='hr' AND salary>5000;

關鍵字 BETWEEN AND查詢

mysql> SELECT name,salary FROM employee5 WHERE salary BETWEEN 5000 AND 15000;

mysql> SELECT name,salary FROM employee5 WHERE salary NOT BETWEEN 5000 AND 15000;

關鍵字 IS NULL 查詢

mysql> SELECT name,job_description FROM employee5 WHERE job_description IS NULL;

mysql> SELECT name,job_description FROM employee5 WHERE job_description IS NOT NULL;

mysql> SELECT name,job_description FROM employee5 WHERE job_description='';

關鍵字IN集合查詢

mysql> SELECT name, salary FROM employee5 WHERE salary=4000 OR salary=5000 OR salary=6000 OR salary=9000 ;

mysql> SELECT name, salary FROM employee5 WHERE salary IN (4000,5000,6000,9000) ;

mysql> SELECT name, salary FROM employee5 WHERE salary NOT IN (4000,5000,6000,9000) ;

關鍵字LIKE模糊查詢

通配符’%’
mysql> SELECT * FROM employee5 WHERE name LIKE 'al%';

通配符’_’
mysql> SELECT * FROM employee5 WHERE name LIKE 'al___';

查詢排序

按單列排序

mysql> SELECT * FROM employee5 ORDER BY salary;

mysql> SELECT name, salary FROM employee5 ORDER BY salary ASC;

mysql> SELECT name, salary FROM employee5 ORDER BY salary DESC;

按多列排序

mysql> SELECT * FROM employee5 ORDER BY hire_date DESC,salary ASC;

# 先按入職時間，再按薪水排序
mysql> SELECT * FROM employee5 ORDER BY hire_date DESC, salary DESC;

# 先按職位，再按薪水排序
mysql> SELECT * FROM employee5 ORDER BY post, salary DESC;

分頁查詢 limit

mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 5;      //默認初始位置為0

mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 0,5;

mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 3,5;      //從第4條開始，共顯示5條

聚合函數查詢

    a、count(*)       表示計算總行數，括號中可以寫*和列名
    b、max(列)        表示求此列的最大值
    c、min(列)        表示求此列的最小值
    d、sun(列)        表示求此列的和
    e、avg(列)        表示求此列的平均值
    
mysql> SELECT COUNT(*) FROM employee5;
mysql> SELECT COUNT(*) FROM employee5 WHERE dep_id=101;
mysql> SELECT MAX(salary) FROM employee5;
mysql> SELECT MIN(salary) FROM employee5;
mysql> SELECT AVG(salary) FROM employee5;
mysql> SELECT SUM(salary) FROM employee5;
mysql> SELECT SUM(salary) FROM employee5 WHERE dep_id=101;

分組查詢

# 單獨使用GROUP BY關鍵字分組
mysql> SELECT post FROM employee5 GROUP BY post;
注意：我們按照post字段分組，那么select查詢的字段只能是post，想要獲取組內的其他相關信息，需要借助函數

GROUP BY關鍵字和group_concat()函數一起使用

# 按照id分組，并查看組內成員
mysql> SELECT dep_id,GROUP_CONCAT(name) FROM employee5 GROUP BY dep_id;

mysql> SELECT dep_id,GROUP_CONCAT(name) as emp_members FROM employee5 GROUP BY dep_id;

GROUP BY和集合函數一起使用

# 按照dep_id 分組， 并計算組內成員工資總和
mysql> SELECT dep_id,SUM(salary) FROM employee5 GROUP BY dep_id;

# 按照dep_id分組，并計算組內成員工資平均值
mysql> SELECT dep_id,AVG(salary) FROM employee5 GROUP BY dep_id;

正則表達式查詢

mysql> SELECT * FROM employee5 WHERE name REGEXP '^j';

mysql> SELECT * FROM employee5 WHERE salary REGEXP '[5]+.*';

mysql> SELECT * FROM employee5 WHERE salary REGEXP '[5]{2}.*';

MySQL實現單表查詢的簡單方法就先給大家講到這里，對于其它相關問題大家想要了解的可以持續關注我們的行業資訊。我們的板塊內容每天都會捕捉一些行業新聞及專業知識分享給大家的。