//select version();
//status; 2:mysql出现下列情况的解决法子
service mysql start
Starting MySQL.................................................
.....................................................The server quit without updating PID file (/var/lib/mysql/localhost.localdomain.pid). [失败]
mysql -uroot -p
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) ---------------------------------------
[root@localhost ~]# ps aux |grep mysq*
root 1562 0.0 0.0 108328 48 ? S 18:25 0:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --pid-file=/var/lib/mysql/localhost.localdomain.pid
mysql 1692 0.0 9.8 1078000 100220 ? Sl 18:25 0:04 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --user=mysql --log-error=/var/lib/mysql/localhost.localdomain.err --pid-file=/var/lib/mysql/localhost.localdomain.pid
root 3691 0.0 0.0 103248 768 pts/2 D+ 19:48 0:00 grep mysq*
[root@localhost ~]# kill 1562
[root@localhost ~]# kill 1692
[root@localhost ~]# kill 3691
分析MySQL重复启动了
---------------------------------------- 3：写了一半又不想执行了 语句结尾加上 \c
mysql> select user()
-> \c 4:创建表
mysql> create table pet (
-> name varchar(20),owner varchar(20),
-> species varchar(20),sex char(1),birth Date, death Date
-> ); 5：展现创建表的语句
--》show create table pet; 6：将指定的文件插入到表中
--》load data local infile '/export/pratice/pet.xt' into table pet; 7：删除表中全部数据（表结构不变）
--》delete from pet;
-------------------------------------------------------------
+----------+--------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+--------+---------+------+------------+------------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Fang | Benny | dog | m | 1990-08-27 | NULL |
| Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 |
| Chirpy | Gwen | bird | f | 1998-09-11 | NULL |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
| Slim | Benny | snake | m | 0996-04-29 | NULL |
+----------+--------+---------+------+------------+------------+
------------------------------------------------------------- 8：更新表中名字为Bowser的生日
--》update pet set birth = '1995-07-02' where name = 'Bowser';
9：查询名字为Bowser的记录（Bowser不计较大小写）
mysql> select * from pet where name = 'Bowser';
+--------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+--------+-------+---------+------+------------+------------+
| Bowser | Diane | dog | m | 1995-07-02 | 1995-07-29 |
+--------+-------+---------+------+------------+------------+ 10：查找生日在1998年以后的特定查询
mysql> select * from pet where birth >= '1998-1-1';
+--------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+--------+-------+---------+------+------------+-------+
| Chirpy | Gwen | bird | f | 1998-09-11 | NULL |
+--------+-------+---------+------+------------+-------+ 11：多条件查询
mysql> select * from pet where species = 'dog' and sex ='f';
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+ mysql> select * from pet where species = 'snake' or species ='bird';
+----------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+-------+
| Chirpy | Gwen | bird | f | 1998-09-11 | NULL |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
| Slim | Benny | snake | m | 0996-04-29 | NULL |
+----------+-------+---------+------+------------+-------+
12：优先执行括号中的逻辑
mysql> select * from pet where (species = 'cat' and sex = 'm')
-> or (species = 'dog' and sex = 'f');
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
13：检索特定的列
mysql> select name,birth from pet;
+----------+------------+
| name | birth |
+----------+------------+
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| Buffy | 1989-05-13 |
| Fang | 1990-08-27 |
| Bowser | 1995-07-02 |
| Chirpy | 1998-09-11 |
| Whistler | 1997-12-09 |
| Slim | 0996-04-29 |
+----------+------------+ 14：查询不复的字段--关键词DISTINCT
mysql> select owner from pet;
+--------+
| owner |
+--------+
| Harold |
| Gwen |
| Harold |
| Benny |
| Diane |
| Gwen |
| Gwen |
| Benny |
+--------+ mysql> select distinct owner from pet;
+--------+
| owner |
+--------+
| Harold |
| Gwen |
| Benny |
| Diane |
+--------+
15:使用组合条件查询特定的列
mysql> select name,species,birth from pet
-> where species = 'dog' or
-> species = 'cat'
-> ;
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Fluffy | cat | 1993-02-04 |
| Claws | cat | 1994-03-17 |
| Buffy | dog | 1989-05-13 |
| Fang | dog | 1990-08-27 |
| Bowser | dog | 1995-07-02 |
+--------+---------+------------+
16：根据某个字段进行排序（默认为升序）
mysql> select name,birth from pet order by birth;
+----------+------------+
| name | birth |
+----------+------------+
| Slim | 0996-04-29 |
| Buffy | 1989-05-13 |
| Fang | 1990-08-27 |
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| Bowser | 1995-07-02 |
| Whistler | 1997-12-09 |
| Chirpy | 1998-09-11 |
+----------+------------+ 升降序排列
select name,birth from pet order by birth desc;
select name,birth from pet order by birth asc;
17：日期计算
--查询当前日期
mysql> select curdate() from pet;
--获取当年的年
mysql> select year('1995-07-02') as years from pet;
18：根据出生日期和现在时间算出年龄
mysql>
SELECT name, birth, CURDATE(),TIMESTAMPDIFF(YEAR,birth,CURDATE())
-> AS age FROM pet;
+----------+------------+------------+------+
| name | birth | CURDATE() | age |
+----------+------------+------------+------+
| Fluffy | 1993-02-04 | 2019-05-05 | 26 |
| Claws | 1994-03-17 | 2019-05-05 | 25 |
| Buffy | 1989-05-13 | 2019-05-05 | 29 |
| Fang | 1990-08-27 | 2019-05-05 | 28 |
| Bowser | 1995-07-02 | 2019-05-05 | 23 |
| Chirpy | 1998-09-11 | 2019-05-05 | 20 |
| Whistler | 1997-12-09 | 2019-05-05 | 21 |
| Slim | 0996-04-29 | 2019-05-05 | 1023 |
+----------+------------+------------+------+
19：NULL与not NULL
mysql> select name,birth,death,
-> TIMESTAMPDIFF(YEAR,birth,death)
-> as age
-> from pet where death is not null
-> order by age;
+--------+------------+------------+------+
| name | birth | death | age |
+--------+------------+------------+------+
| Bowser | 1995-07-02 | 1995-07-29 | 0 |
+--------+------------+------------+------+ mysql> select name,birth,death, TIMESTAMPDIFF(YEAR,birth,death) as age from pet where death is null order by age;
+----------+------------+-------+------+
| name | birth | death | age |
+----------+------------+-------+------+
| Fluffy | 1993-02-04 | NULL | NULL |
| Claws | 1994-03-17 | NULL | NULL |
| Buffy | 1989-05-13 | NULL | NULL |
| Fang | 1990-08-27 | NULL | NULL |
| Chirpy | 1998-09-11 | NULL | NULL |
| Whistler | 1997-12-09 | NULL | NULL |
| Slim | 0996-04-29 | NULL | NULL |
+----------+------------+-------+------+
20：查看mysql字符集
show variables like 'character%';
mysql> show variables like 'character%';
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+ 添加配置
[root@localhost etc]# vim /etc/my.cnf
[mysqld]
character-set-server=utf8
collation-server=utf8_general_ci
sql_mode='NO_ENGINE_SUBSTITUTION' [mysql]
default-character-set = utf8 [mysql.server]
default-character-set = utf8 [mysqld_safe]
default-character-set = utf8 [client]
default-character-set = utf8 重启mysql
service MySQL restart mysql> show variables like 'character%';
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
21：