1、簡單數據記錄查詢
【語法】
select 字段名 from 表名;
（1）查詢所有字段數據
mysql> select empno,ename,job,MSG,Hiredate,sal,comm,deptno from t_employee;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
+-------+--------+-------+------+------------+--------+------+--------+
4 rows in set (0.11 sec)
mysql> select * from t_employee;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
+-------+--------+-------+------+------------+--------+------+--------+
4 rows in set (0.00 sec)
（2）查詢指定字段數據
mysql> select ename,comm from t_employee;
+--------+------+
| ename | comm |
+--------+------+
| SMITH | NULL |
| ename1 | 1.00 |
| ename2 | 2.00 |
| ename3 | 3.00 |
+--------+------+
4 rows in set (0.00 sec)
（3）避免重複數據查詢-distinct
mysql> select distinct ename from t_employee;
+--------+
| ename |
+--------+
| SMITH |
| ename1 |
| ename2 |
| ename3 |
+--------+
4 rows in set (0.08 sec)
（4）實現數學四則運算數據查詢
mysql> select ename,sal*12 from t_employee;
+--------+---------+
| ename | sal*12 |
+--------+---------+
| SMITH | 9600.00 |
| ename1 | 12.00 |
| ename2 | 24.00 |
| ename3 | 36.00 |
| ename1 | 24.00 |
+--------+---------+
5 rows in set (0.04 sec)
#使用as給字段sal * 12重命名爲yearsalary顯示
mysql> select ename,sal * 12 as yearsalary from t_employee;
+--------+------------+
| ename | yearsalary |
+--------+------------+
| SMITH | 9600.00 |
| ename1 | 12.00 |
| ename2 | 24.00 |
| ename3 | 36.00 |
| ename1 | 24.00 |
+--------+------------+
5 rows in set (0.00 sec)
（5）設置顯示格式數據查詢
mysql> select concat(ename,'’s annual salary is :',sal * 12) yearsalary from t_employee;
+-------------------------------------+
| yearsalary |
+-------------------------------------+
| SMITH’s annual salary is :9600.00 |
| ename1’s annual salary is :12.00 |
| ename2’s annual salary is :24.00 |
| ename3’s annual salary is :36.00 |
| ename1’s annual salary is :24.00 |
+-------------------------------------+
5 rows in set (0.00 sec)
2、條件數據記錄查詢
【語法】
select 字段名 from 表名 where 條件語句;
（1）帶關係運算符和邏輯運算符的條件數據查詢
- 單條件數據查詢
mysql> select ename from t_employee where job='job2';
+--------+
| ename |
+--------+
| ename2 |
+--------+
1 row in set (0.00 sec)
- 多條件數據查詢
mysql> select ename from t_employee where job='job1'&&sal>1;
+--------+
| ename |
+--------+
| ename1 |
+--------+
1 row in set (0.00 sec)
（2）帶between and關鍵字的範圍查詢
【語法】
select 字段名 from 表名 where between value1 and value2;
- 符合範圍的數據記錄查詢
mysql> select ename from t_employee where sal between 2 and 3;
+--------+
| ename |
+--------+
| ename2 |
| ename3 |
| ename1 |
+--------+
3 rows in set (0.00 sec)
- 不符合範圍的數據記錄查詢
mysql> select ename from t_employee where sal not between 2 and 3;
+--------+
| ename |
+--------+
| SMITH |
| ename1 |
+--------+
2 rows in set (0.00 sec)
（3）帶is null 關鍵字的空值查詢
【語法】
select 字段名 from 表名 where 字段名 is null;
- 空值數據記錄查詢
mysql> select ename from t_employee where comm is null;
+-------+
| ename |
+-------+
| SMITH |
+-------+
1 row in set (0.00 sec)
- 不是空值數據記錄查詢
mysql> select ename from t_employee where not comm is null;
+--------+
| ename |
+--------+
| ename1 |
| ename2 |
| ename3 |
| ename1 |
+--------+
4 rows in set (0.00 sec)
（4）帶in關鍵字的集合查詢
【語法】
select 字段名 from 表名 where field in (value1,value2……,valuen);
- 在集合中數據記錄查詢
mysql> select ename from t_employee where sal in (2,7,8);
+--------+
| ename |
+--------+
| ename2 |
| ename1 |
+--------+
2 rows in set (0.00 sec)
mysql> select ename from t_employee where sal=2 or sal=7 or sal=8;
+--------+
| ename |
+--------+
| ename2 |
| ename1 |
+--------+
2 rows in set (0.00 sec)
- 不在集合中數據記錄查詢
mysql> select ename from t_employee where not sal in (2,7,8);
+--------+
| ename |
+--------+
| SMITH |
| ename1 |
| ename3 |
+--------+
3 rows in set (0.01 sec)
mysql> select ename from t_employee where sal not in (2,7,8);
+--------+
| ename |
+--------+
| SMITH |
| ename1 |
| ename3 |
+--------+
3 rows in set (0.00 sec)
- 關於集合查詢注意點
#使用關鍵字in時，查詢集合中存在null，不影響查詢
mysql> select ename from t_employee where sal in (2,7,8,null);
+--------+
| ename |
+--------+
| ename2 |
| ename1 |
+--------+
2 rows in set (0.00 sec)
#使用關鍵字not in時，查詢集合中存在null，不會有任何查詢結果
mysql> select ename from t_employee where sal not in (2,7,8,null);
Empty set (0.00 sec)
（5）帶like關鍵字的模糊查詢
【語法】
select 字段名 from 表名 where field like value;
- 帶有”%“通配符的查詢（該通配符能夠匹配任意長度的字符串）
mysql> select ename from t_employee where ename like 'e%';
+--------+
| ename |
+--------+
| ename1 |
| ename2 |
| ename3 |
| ename1 |
+--------+
4 rows in set (0.00 sec)
mysql> select ename from t_employee where ename not like 'e%';
+-------+
| ename |
+-------+
| SMITH |
+-------+
1 row in set (0.18 sec)
- 帶有”_“通配符的查詢（該通配符能匹配單個字符）
mysql> select ename from t_employee where ename like '_n%';
+--------+
| ename |
+--------+
| ename1 |
| ename2 |
| ename3 |
| ename1 |
+--------+
4 rows in set (0.00 sec)
mysql> select ename from t_employee where ename not like '_n%';
+-------+
| ename |
+-------+
| SMITH |
+-------+
1 row in set (0.00 sec)
（5）排序數據記錄查詢
【語法】
select 字段名 from 表名 where 條件語句 order by 字段 [asc|desc];
- 按照單子段排序
#升序排序
mysql> select * from t_employee order by sal;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 1 | ename1 | job1 | 3 | 2019-03-12 | 2.00 | 3.00 | 3 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+--------+-------+------+------------+--------+------+--------+
5 rows in set (0.06 sec)
mysql> select * from t_employee order by sal asc;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 1 | ename1 | job1 | 3 | 2019-03-12 | 2.00 | 3.00 | 3 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+--------+-------+------+------------+--------+------+--------+
5 rows in set (0.00 sec)
#降序排序
mysql> select * from t_employee order by sal desc;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 1 | ename1 | job1 | 3 | 2019-03-12 | 2.00 | 3.00 | 3 |
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
+-------+--------+-------+------+------------+--------+------+--------+
5 rows in set (0.00 sec)
- 按照多字段排序
mysql> select * from t_employee order by sal,MSG desc;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 1 | ename1 | job1 | 3 | 2019-03-12 | 2.00 | 3.00 | 3 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+--------+-------+------+------------+--------+------+--------+
5 rows in set (0.00 sec)
mysql> select * from t_employee order by sal asc ,MSG desc;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 1 | ename1 | job1 | 3 | 2019-03-12 | 2.00 | 3.00 | 3 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 2.00 | 2 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+--------+-------+------+------------+--------+------+--------+
5 rows in set (0.00 sec)
- 限制數據記錄查詢數量
【語法】
select 字段名 from 表名 where 條件語句 limit offset_start,row_count;
（1）不指定初始位置
mysql> select * from t_employee where comm is null limit 2;
+-------+-------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+-------+-------+------+------------+--------+------+--------+
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+-------+-------+------+------------+--------+------+--------+
1 row in set (0.01 sec)
（2）指定初始位置
mysql> select * from t_employee where comm is null order by MSG limit 0,5;
+-------+-------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+-------+-------+------+------------+--------+------+--------+
| 73 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 69 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+-------+-------+------+------------+--------+------+--------+
3 rows in set (0.06 sec)
mysql> select * from t_employee where comm is null order by MSG limit 5,10;
+-------+-------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+-------+-------+------+------------+--------+------+--------+
| 73 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 73 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 7369 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 69 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
| 73 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | NULL | 20 |
+-------+-------+-------+------+------------+--------+------+--------+
5 rows in set (0.00 sec)
4、統計函數和分組數據記錄查詢
【語法】
select 統計函數(字段) from 表名 where 條件語句;
【統計函數】
- count()函數：統計表中記錄的條數 avg()函數：計算字段值的平均值
- sum()函數：計算字段值的總和
- max()函數：查詢字段值的最大值
- min()函數：查詢字段值的最小值
- 如果所操作的表裏沒有任何數據，則count()函數返回數據0，其他函數則返回null
（1）mysql支持的統計函數
- 統計數據記錄條數
mysql> select count(*) number from t_employee;
+--------+
| number |
+--------+
| 14 |
+--------+
1 row in set (0.00 sec)
mysql> select count(comm) number from t_employee;
+--------+
| number |
+--------+
| 4 |
+--------+
1 row in set (0.00 sec)
mysql> select count(comm) number from t_employee where not comm=0;
+--------+
| number |
+--------+
| 3 |
+--------+
1 row in set (0.00 sec)
- 統計計算平均值
mysql> select avg(comm) average from t_employee where not comm=0;
+----------+
| average |
+----------+
| 2.333333 |
+----------+
1 row in set (0.00 sec)
- 統計計算求和
mysql> select sum(comm) sumvalue from t_employee where not comm=0;
+----------+
| sumvalue |
+----------+
| 7.00 |
+----------+
1 row in set (0.00 sec)
- 統計計算最大值和最小值
mysql> select max(sal) maxval,min(sal) minval from t_employee;
+--------+--------+
| maxval | minval |
+--------+--------+
| 800.00 | 1.00 |
+--------+--------+
1 row in set (0.01 sec)
（2）分組數據查詢
- 簡單分組查詢（分組中顯示的數據記錄爲隨機的）
【語法】
select 統計函數 from 表名 where 條件語句 group by 字段名;
【實例】
mysql> select * from t_employee group by deptno;
+-------+--------+-------+------+------------+--------+------+--------+
| empno | ename | job | MSG | Hiredate | sal | comm | deptno |
+-------+--------+-------+------+------------+--------+------+--------+
| 1 | ename1 | job1 | 1 | 2019-03-12 | 1.00 | 1.00 | 1 |
| 2 | ename2 | job2 | 2 | 2019-03-12 | 2.00 | 0.00 | 2 |
| 3 | ename3 | job3 | 3 | 2019-03-12 | 3.00 | 3.00 | 3 |
| 73 | SMITH | CLERK | 7902 | 2019-03-12 | 800.00 | 0.00 | 20 |
+-------+--------+-------+------+------------+--------+------+--------+
4 rows in set (0.01 sec)
- 實現統計功能分組查詢
【語法】
select group_concat(字段名) from 表名 where 條件語句 group by 字段名;
【實例】
mysql> select deptno,group_concat(ename) enames,count(ename) number
-> from t_employee group by deptno;
+--------+-------------------------------------------------------+--------+
| deptno | enames | number |
+--------+-------------------------------------------------------+--------+
| 1 | ename1 | 1 |
| 2 | ename2 | 1 |
| 3 | ename3,ename1 | 2 |
| 20 | SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH | 9 |
+--------+-------------------------------------------------------+--------+
4 rows in set (0.06 sec)
- 實現多個字段分組查詢
【語法】
select group_concat(field),function(field) from 表名 where 條件語句 group by field1……fieldn;
【實例】
mysql> select deptno,MSG,group_concat(ename) enames,count(ename) number
-> from t_employee group by deptno,MSG;
+--------+------+-------------------------------------------------------+--------+
| deptno | MSG | enames | number |
+--------+------+-------------------------------------------------------+--------+
| 1 | 1 | ename1 | 1 |
| 2 | 2 | ename2 | 1 |
| 3 | 3 | ename3,ename1 | 2 |
| 20 | 7902 | SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH | 9 |
+--------+------+-------------------------------------------------------+--------+
4 rows in set (0.00 sec)
- 實現having子句限定分組查詢
【語法】
select function(field) from 表名 where 條件語句 group by field1……fieldn having 條件語句;
【實例】
mysql> select deptno,avg(sal) average,group_concat(ename) enames,count(ename) number
-> from t_employee
-> group by deptno
-> having avg(sal) > 3;
+--------+------------+-------------------------------------------------------+--------+
| deptno | average | enames | number |
+--------+------------+-------------------------------------------------------+--------+
| 20 | 800.000000 | SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH,SMITH | 9 |
+--------+------------+-------------------------------------------------------+--------+
1 row in set (0.09 sec)