所需要用到的創(chuàng)建表格的代碼如下：

create table dept
(
deptno numeric(2),
dname varchar(14),
loc varchar(13),
constraint pk_dept primary key(deptno)
);
create table emp
(
empno numeric(4),
ename varchar(10),
job varchar(9),
mgr numeric(4),
hiredate date,
sal numeric(7,2),
comm numeric(7,2),
deptno numeric(2),
constraint pk_emp primary key(empno),
constraint fk_deptno foreign key(deptno) references dept(deptno)
);
insert into dept values(10,'ACCOUNTING','NEW YORK');
insert into dept values (20,'RESEARCH','DALLAS');
insert into dept values (30,'SALES','CHICAGO');
insert into dept values (40,'OPERATIONS','BOSTON');
insert into emp values(7369,'SMITH','CLERK',7902,'1980-12-17',800,NULL,20);
insert into emp values (7499,'ALLEN','SALESMAN',7698,'1981-02-02',1600,300,30);
insert into emp values (7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30);
insert into emp values (7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20);
insert into emp values (7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30);
insert into emp values (7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30);
insert into emp values (7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10);
insert into emp
values (7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10);
insert into emp values (7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,0,30);
insert into emp values (7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30);
insert into emp values (7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20);
insert into emp values (7934,'MILLER','CLERK',7782,'1982-01-23',1300,NULL,10);

表視圖：

emp表結(jié)構(gòu)

emp表視圖

dept表結(jié)構(gòu)

dept表視圖

Mysql簡單select句子

列出管理MySQL數(shù)據(jù)庫服務的常用命令：
Systemctl start/stop/status/restart mysql

#用root用戶連接數(shù)據(jù)庫，查詢當前有哪些數(shù)據(jù)庫
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

#創(chuàng)建db數(shù)據(jù)庫，執(zhí)行scott.sql腳本文件，創(chuàng)建測試表emp和dept
mysql> create database db;
Query OK, 1 row affected (0.07 sec)
mysql> use db
Database changed
mysql> source scott.sql

#連接db數(shù)據(jù)庫，查詢db數(shù)據(jù)庫中有哪些表
mysql> show tables;
+--------------+
| Tables_in_db |
+--------------+
| dept         |
| emp          |
+--------------+
2 rows in set (0.00 sec)

#查看emp和dept表的結(jié)構(gòu)。
mysql> desc dept;（查詢表dept結(jié)構(gòu)）
+--------+--------------+------+-----+---------+-------+
| Field  | Type         | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+-------+
| deptno | decimal(2,0) | NO   | PRI | NULL    |       |
| dname  | varchar(14)  | YES  |     | NULL    |       |
| loc    | varchar(13)  | YES  |     | NULL    |       |
+--------+--------------+------+-----+---------+-------+
3 rows in set (0.01 sec)
mysql> desc emp;（查詢表emp結(jié)構(gòu)）
+----------+--------------+------+-----+---------+-------+
| Field    | Type         | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| empno    | decimal(4,0) | NO   | PRI | NULL    |       |
| ename    | varchar(10)  | YES  |     | NULL    |       |
| job      | varchar(9)   | YES  |     | NULL    |       |
| mgr      | decimal(4,0) | YES  |     | NULL    |       |
| hiredate | datetime     | YES  |     | NULL    |       |
| sal      | decimal(7,2) | YES  |     | NULL    |       |
| comm     | decimal(7,2) | YES  |     | NULL    |       |
| deptno   | decimal(2,0) | YES  | MUL | NULL    |       |
+----------+--------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

#連接db數(shù)據(jù)庫，查詢emp表中的所有人的姓名。
mysql> select ename from emp;
+--------+
| ename  |
+--------+
| SMITH  |
| ALLEN  |
| WARD   |
| JONES  |
| MARTIN |
| BLAKE  |
| CLARK  |
| KING   |
| TURNER |
| JAMES  |
| FORD   |
| MILLER |
+--------+
12 rows in set (0.00 sec)

#用別名把上面查詢結(jié)果中的列名ename改為漢字：員工名稱。
mysql> select ename as 員工名稱；
     -> from emp;
+-----------------+
| 員工名稱；      |
+-----------------+
| SMITH           |
| ALLEN           |
| WARD            |
| JONES           |
| MARTIN          |
| BLAKE           |
| CLARK           |
| KING            |
| TURNER          |
| JAMES           |
| FORD            |
| MILLER          |
+-----------------+
12 rows in set (0.00 sec)

#查詢emp表中的不重復的部門號。
mysql> select distinct deptno from emp;
+--------+
| deptno |
+--------+
|     10 |
|     20 |
|     30 |
+--------+
3 rows in set (0.00 sec)

#查詢emp表中，工資額大于2000的員工的姓名及其工資額。
mysql> select ename,sal from emp where sal > 2000;
+-------+---------+
| ename | sal     |
+-------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| KING  | 5000.00 |
| FORD  | 3000.00 |
+-------+---------+

#查詢emp表中，工資額界于2000與3000之間的員工姓名及其工資額。
方法一：
mysql> select ename,sal from emp where sal >= 2000 and sal <= 3000;
+-------+---------+
| ename | sal     |
+-------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| FORD  | 3000.00 |
+-------+---------+
4 rows in set (0.00 sec)
方法二：
mysql> select ename,sal from emp where sal between 2000 and 3000;
+-------+---------+
| ename | sal     |
+-------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| FORD  | 3000.00 |
+-------+---------+
4 rows in set (0.00 sec)

#查詢emp表中，ename列以字母A開頭的員工的姓名。
mysql> select ename,sal from emp where ename like 'A%';
+-------+---------+
| ename | sal     |
+-------+---------+
| ALLEN | 1600.00 |
+-------+---------+
1 row in set (0.00 sec)

#查詢emp表中，ename列含有字母A的員工的姓名。
   mysql> select ename,sal from emp where ename like '%A%';
+--------+---------+
| ename  | sal     |
+--------+---------+
| ALLEN  | 1600.00 |
| WARD   | 1250.00 |
| MARTIN | 1250.00 |
| BLAKE  | 2850.00 |
| CLARK  | 2450.00 |
| JAMES  |  950.00 |
+--------+---------+
6 rows in set (0.00 sec)

#查詢emp表中，ename列第三個字母為A、第五個字母為R的員工的姓名。
mysql> select ename,sal from emp where ename like '__A_R%';
Empty set (0.00 sec)

#查詢emp表中，姓名及工資額，要求工資按照降序排序。
mysql> select ename,sal(從低到高)
-> from emp
-> order by sal;
+--------+---------+
| ename  | sal     |
+--------+---------+
| SMITH  |  800.00 |
| JAMES  |  950.00 |
| WARD   | 1250.00 |
| MARTIN | 1250.00 |
| MILLER | 1300.00 |
| TURNER | 1500.00 |
| ALLEN  | 1600.00 |
| CLARK  | 2450.00 |
| BLAKE  | 2850.00 |
| JONES  | 2975.00 |
| FORD   | 3000.00 |
| KING   | 5000.00 |
+--------+---------+
12 rows in set (0.00 sec)
mysql> select ename,sal from emp order by sal desc;（叢高到低）
+--------+---------+
| ename  | sal     |
+--------+---------+
| KING   | 5000.00 |
| FORD   | 3000.00 |
| JONES  | 2975.00 |
| BLAKE  | 2850.00 |
| CLARK  | 2450.00 |
| ALLEN  | 1600.00 |
| TURNER | 1500.00 |
| MILLER | 1300.00 |
| WARD   | 1250.00 |
| MARTIN | 1250.00 |
| JAMES  |  950.00 |
| SMITH  |  800.00 |
+--------+---------+
12 rows in set (0.00 sec)

#查詢emp表中，comm列為NULL的員工的姓名。
mysql> select ename from emp where comm is null;
+--------+
| ename  |
+--------+
| SMITH  |
| JONES  |
| BLAKE  |
| CLARK  |
| KING   |
| JAMES  |
| FORD   |
| MILLER |
+--------+
8 rows in set (0.00 sec)

mysql> select ename from emp where comm is not null;
+--------+
| ename  |
+--------+
| ALLEN  |
| WARD   |
| MARTIN |
| TURNER |
+--------+
4 rows in set (0.00 sec)

匯總函數(shù)

#查詢每個部門的最高工資，要求列出部門編號及其最高工資額。
mysql> select deptno,max(sal) from emp group by deptno;
+--------+----------+
| deptno | max(sal) |
+--------+----------+
|     10 |  5000.00 |
|     20 |  3000.00 |
|     30 |  2850.00 |
+--------+----------+
3 rows in set (0.00 sec)

#查詢各個工種的人數(shù)。
mysql> select job 工種,count(empno) 員工人數(shù) from emp group by job;
+-----------+--------------+
| 工種      | 員工人數(shù)     |
+-----------+--------------+
| CLERK     |            3 |
| SALESMAN  |            4 |
| MANAGER   |            3 |
| PRESIDENT |            1 |
| ANALYST   |            1 |
+-----------+--------------+
5 rows in set (0.00 sec)

#查詢sal列上有無重復值，給出判斷語句及判斷結(jié)果。
方法一：
mysql> select sal,count(sal) from emp group by sal having count(sal);
+---------+------------+
| sal     | count(sal) |
+---------+------------+
|  800.00 |          1 |
| 1600.00 |          1 |
| 1250.00 |          2 |
| 2975.00 |          1 |
| 2850.00 |          1 |
| 2450.00 |          1 |
| 5000.00 |          1 |
| 1500.00 |          1 |
|  950.00 |          1 |
| 3000.00 |          1 |
| 1300.00 |          1 |
+---------+------------+
11 rows in set (0.00 sec)
方法二：
mysql> select sal,count(*) from emp group by sal having count(sal)>1;
+---------+----------+
| sal     | count(*) |
+---------+----------+
| 1250.00 |        2 |
+---------+----------+
1 row in set (0.00 sec)

#查詢每個員工工資與emp表的平均工資之間的差距。
mysql> select ename,sal - (select avg(sal) from emp) from emp;
+--------+----------------------------------+
| ename  | sal - (select avg(sal) from emp) |
+--------+----------------------------------+
| SMITH  |                     -1277.083333 |
| ALLEN  |                      -477.083333 |
| WARD   |                      -827.083333 |
| JONES  |                       897.916667 |
| MARTIN |                      -827.083333 |
| BLAKE  |                       772.916667 |
| CLARK  |                       372.916667 |
| KING   |                      2922.916667 |
| TURNER |                      -577.083333 |
| JAMES  |                     -1127.083333 |
| FORD   |                       922.916667 |
| MILLER |                      -777.083333 |
+--------+----------------------------------+
12 rows in set (0.00 sec)

mysql> select sal,count(*) from emp group by sal having count(sal)>1;
+---------+----------+
| sal     | count(*) |
+---------+----------+
| 1250.00 |        2 |
+---------+----------+
1 row in set (0.00 sec)

#查詢emp表最高工資與平均工資的差距。
mysql> select max(sal) - (select avg(sal) from emp) from emp;
+---------------------------------------+
| max(sal) - (select avg(sal) from emp) |
+---------------------------------------+
|                           2922.916667 |
+---------------------------------------+
1 row in set (0.00 sec)

#查詢每個員工的名稱及其工種的名稱。
mysql> select ename,job from emp;
+--------+-----------+
| ename  | job       |
+--------+-----------+
| SMITH  | CLERK     |
| ALLEN  | SALESMAN  |
| WARD   | SALESMAN  |
| JONES  | MANAGER   |
| MARTIN | SALESMAN  |
| BLAKE  | MANAGER   |
| CLARK  | MANAGER   |
| KING   | PRESIDENT |
| TURNER | SALESMAN  |
| JAMES  | CLERK     |
| FORD   | ANALYST   |
| MILLER | CLERK     |
+--------+-----------+
12 rows in set (0.00 sec)

#查詢哪個工種的人數(shù)最多，要求列出這種工種的完整名稱及其人數(shù)。
方法一：
mysql> select job,count(1) from emp group by job;
+-----------+----------+
| job       | count(1) |
+-----------+----------+
| CLERK     |        3 |
| SALESMAN  |        4 |
| MANAGER   |        3 |
| PRESIDENT |        1 |
| ANALYST   |        1 |
+-----------+----------+
5 rows in set (0.00 sec)
方法二：
mysql> select job,count(*) from emp group by job order by count(*) desc limit 1;
+----------+----------+
| job      | count(*) |
+----------+----------+
| SALESMAN |        4 |
+----------+----------+
1 row in set (0.00 sec)

#查詢哪個部門的員工個數(shù)最多，要求列出此部門編號及其員工個數(shù)。
mysql> select deptno,count(*) from emp group by deptno order by count(*) desc limit 1;
+--------+----------+
| deptno | count(*) |
+--------+----------+
|     30 |        6 |
+--------+----------+
1 row in set (0.01 sec)

#查詢每年的入職人數(shù)，要求列出相應年份及入職人數(shù)，查詢結(jié)果以年份排序。
mysql> select year(hiredate),count(*) from emp group by year(hiredate) order   
        by year(hiredate) asc;
+----------------+----------+
| year(hiredate) | count(*) |
+----------------+----------+
|           1980 |        1 |
|           1981 |       10 |
|           1982 |        1 |
+----------------+----------+
3 rows in set (0.00 sec)

#查詢哪個部門的平均工資最高，要求列出部門名稱及其平均工資額。
mysql> select deptno,avg(sal) from emp group by deptno;
+--------+-------------+
| deptno | avg(sal)    |
+--------+-------------+
|     10 | 2916.666667 |
|     20 | 2258.333333 |
|     30 | 1566.666667 |
+--------+-------------+
3 rows in set (0.00 sec

#查詢哪些工種的平均工資高于2000，要求列出工種名稱及其平均工資額。
mysql> select avg(sal),job from emp group by job having avg(sal)>2000;
+-------------+-----------+
| avg(sal)    | job       |
+-------------+-----------+
| 2758.333333 | MANAGER   |
| 5000.000000 | PRESIDENT |
| 3000.000000 | ANALYST   |
+-------------+-----------+
3 rows in set (0.00 sec)

#利用find命令(或其他命令)，查詢mysql和mysqld在哪個目錄下。
Mysql：
[root@law ~]# find / -iname mysql
/etc/logrotate.d/mysql
/etc/selinux/targeted/active/modules/100/mysql
/var/lib/mysql
/var/lib/mysql/mysql
/usr/bin/mysql
/usr/lib64/mysql
Mysqld：
[root@law ~]# find / -iname mysqld
/run/mysqld
/usr/sbin/mysqld

查詢

# 查詢每個部門分別是哪個員工獲得了其所在部門的最高工資，要求列出其名稱、部門名稱及其工資額。
select e.ename,dept.dname,a.max_sal
from
emp e,
dept,
(select deptno,max(sal) as max_sal from emp group by deptno) a
where
e.deptno = dept.deptno
and
a.deptno = e.deptno
and
a.max_sal = e.sal
結(jié)果：
+-------+------------+---------+
| ename | dname | max_sal |
+-------+------------+---------+
| KING | ACCOUNTING | 5000.00 |
| FORD | RESEARCH | 3000.00 |
| BLAKE | SALES | 2850.00 |
+-------+------------+---------+
3 rows in set (0.00 sec)

#查詢工資超過平均工資的員工個數(shù)
mysql> select count(sal) from emp where sal>(select avg(sal) from emp);         +------------+
| count(sal) |
+------------+
|          5 |
+------------+
1 row in set (0.00 sec)

#查詢每個部門中，超過部門平均工資的員工姓名。
select deptno,ename from emp
where
sal>(select avg(sal) from emp where emp.deptno = deptno)
結(jié)果：
+--------+-------+
| deptno | ename |
+--------+-------+
|     20 | JONES |
|     30 | BLAKE |
|     10 | CLARK |
|     10 | KING  |
|     20 | FORD  |
+--------+-------+
5 rows in set (0.00 sec)

索引

#在emp表的ename列創(chuàng)建索引idx_ename，確認索引已創(chuàng)建。
mysql> create index idx_ename on emp(ename);
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> show index from emp\G;
*************************** 1. row ***************************
        Table: emp
   Non_unique: 1
     Key_name: idx_ename
 Seq_in_index: 1
  Column_name: ename
    Collation: A
  Cardinality: 12
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment:
Index_comment:
      Visible: YES
1 row in set (0.00 sec)

ERROR:
No query specified

#執(zhí)行下面命令對emp表添加一行記錄：
mysql> insert into emp(empno, ename, sal, deptno)
-> values(9999, 'MIKE', 3000.00, 10);
重新執(zhí)行show index from emp，查看索引的Cardinality是否變化，說明了什么問題。執(zhí)行下面命令對emp表重新計算統(tǒng)計信息，再次查詢其Cardinality是否變化。
mysql> analyze table emp;
重新分析

#查看下面查詢的執(zhí)行計劃，確認其是否使用了idx_ename索引。
#select * from emp where ename = 'SMITH'
mysql> explain select * from emp where ename = 'SMITH'\G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: emp
   partitions: NULL
         type: ref
possible_keys: idx_ename
          key: idx_ename
      key_len: 43
          ref: const
         rows: 1
     filtered: 100.00
        Extra: NULL
1 row in set, 1 warning (0.00 sec)
ERROR:
No query specified

#select * from emp where ename like 'S%'
mysql> explain select * from emp where ename like 'S%'\G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: emp
   partitions: NULL
         type: range
possible_keys: idx_ename
          key: idx_ename
      key_len: 43
          ref: NULL
         rows: 1
     filtered: 100.00
        Extra: Using index condition
1 row in set, 1 warning (0.04 sec)
ERROR:
No query specified

#select * from emp where ename like '%S'
mysql> explain select * from emp where ename like '%S'\G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: emp
   partitions: NULL
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 13
     filtered: 11.11
        Extra: Using where
1 row in set, 1 warning (0.00 sec)
ERROR:
No query specified

#刪除idx_ename索引。
mysql> drop index idx_ename on emp;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

#執(zhí)行下面命令在ename和sal列上創(chuàng)建復合索引idx_ename_sal，確認索引已創(chuàng)建。
mysql> create index idx_ename_sal on emp(ename, sal);

#下面哪個查詢會使用以上idx_ename_sal。
select * from emp where ename = 'SMITH'
select * from emp where sal = 1000
select * from emp where ename = 'SMITH' and sal = 1000
select * from emp where sal = 1000 and ename = 'SMITH'

#下面命令，查看表連接的執(zhí)行計劃。
mysql> explain
    -> select e.ename, d.dname
    -> from emp e, dept d
    -> where e.deptno = d.deptno
    -> \G

#創(chuàng)建big_table存儲過程后，執(zhí)行call big_table(100000)，創(chuàng)建big_table表，并對其添加10萬行記錄，在id列上創(chuàng)建索引idx_id，下面查詢是否會用到此索引：
mysql>select big_table from t where id = 1000
#執(zhí)行下面update命令：
mysql>update big_table set id = 1000 where id >= 1001;
#執(zhí)行下面命令重新計算big_table的統(tǒng)計信息：
mysql> analyze table big_table;
#再次查看下面命令是否使用了idx_id索引：
mysql>select * from big_table where id = 1000
#執(zhí)行下面命令統(tǒng)計id列的直方圖后，以上查詢是否會使用索引
mysql> analyze table big_table update histogram on length with 1000 buckets;

邏輯備份

#執(zhí)行select into outfile導出dept表，清空dept表后由邏輯備份執(zhí)行l(wèi)oad data導入數(shù)據(jù)。
mysql> select * from dept into outfile '/var/lib/mysql-files/dept.ckp'
    -> ;
Query OK, 4 rows affected (0.00 sec)
mysql> truncate table dept;
Query OK, 0 rows affected (0.06 sec)
mysql> select * from dept;
Empty set (0.00 sec)
mysql> edit
    -> \p
--------------
load data infile '/var/lib/mysql-files/dept.ckp'
into table dept
--------------
    -> ;
Query OK, 4 rows affected (0.10 sec)
Records: 4  Deleted: 0  Skipped: 0  Warnings: 0
mysql> select * from dept;
+--------+------------+----------+
| deptno | dname      | loc      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+
4 rows in set (0.00 sec)
[root@law mysql-files]# ls
dept_bak.CSV  dept.bkp  dept.ckp  dept.sql  dept.txt
[root@law mysql-files]# cat dept.ckp
10      ACCOUNTING      NEW YORK
20      RESEARCH        DALLAS
30      SALES   CHICAGO
40      OPERATIONS      BOSTON

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