MySQL 系列（二） 你不知道的数据库操作——1

# 插入单条数据
        insert into 表 (列名,列名...) values (值,值,值...)
# 插入多条数据
       insert into 表 (列名,列名...) values (值,值,值...),(值,值,值...)
# 插入另一条语句的查询结果
        insert into 表 (列名,列名...) select 列名,列名... from 表
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delete from 表;
delete from 表 where id＝1;
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update 表 set name ＝ 'nick' where id>1
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select * from 表
select * from 表 where id > 1
select nid,name,gender as gg from 表 where id > 1


# as 做别名
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select * from 表 where id > 1 and name != 'nick' and num = 12;    # 多个条件
    select * from 表 where id between 5 and 16;                       # id在5到16之间
    select * from 表 where id in (11,22,33);                          # id在元祖中
    select * from 表 where id not in (11,22,33);                      # id不在元祖中
    select * from 表 where id in (select nid from 表);                # id在查询结果中
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    select * from 表 where name like 'ni%'  # ni开头的所有（多个字符串）
    select * from 表 where name like 's_'   # s开头的所有（一个字符）
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    select * from 表 limit 5;            # 前5行
    select * from 表 limit 9,5;          # 从第9行开始的5行
    select * from 表 limit 5 offset 9    # 从第9行开始的5行
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    select * from 表 order by 列 asc             # 根据 “列” 从小到大排列
    select * from 表 order by 列 desc            # 根据 “列” 从大到小排列
    select * from 表 order by 列1 desc,列2 asc   # 根据 “列1” 从大到小排列，如果相同则按列2从小到大排序
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    select num from 表 group by num           # 根据num分组
    select num,nid from 表 group by num,nid   # 根据num和nid分组
    select num,nid from 表  where nid > 10 group by num,nid order nid desc
    select num,nid,count(*),sum(score),max(score),min(score) from 表 group by num,nid  # 内置函数
    select num from 表 group by num having max(id) > 10    # 前面计算的结果交由后面处理
 
    注：group by 必须在where之后，order by之前
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count(*)、count(1) # 表示个数
sum(score)     　  # 表示和
max(score)     　  # 表示最大数
min(score)     　  # 表示最小数




having            # 要用前面处理结果是用having。
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无对应关系则不显示
    select A.num, A.name, B.name
    from A,B
    Where A.nid = B.nid
 
    无对应关系则不显示
    select A.num, A.name, B.name
    from A inner join B
    on A.nid = B.nid
 
    A表所有显示，如果B中无对应关系，则值为null
    select A.num, A.name, B.name
    from A left join B
    on A.nid = B.nid
 
    B表所有显示，如果B中无对应关系，则值为null
    select A.num, A.name, B.name
    from A right join B
    on A.nid = B.nid
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    组合，自动处理重合
    select nickname
    from A
    union
    select name
    from B
 
    组合，不处理重合
    select nickname
    from A
    union all
    select name
    from B
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1>    命令语法：select<字段1，字段2，…>from<表名>where<表达式>
2>    查询所有
mysql> select * from student;
+----+-----------------+------+--------+
| id | name     | age | dept |
+----+-----------------+-------+--------+
|  2 | oldsuo   |   0 | NULL |
|  3 | kangknag |   0 | NULL |
|  4 | kangkang |   0 | NULL |
+----+-----------------+-------+--------+
3 rows in set (0.00 sec)
3>    查询某列。不用*，查询的列列出来。
mysql> select id,name from student;
+----+----------------+
| id | name    |
+----+----------------+
|  2 | oldsuo  |
|  3 | kangknag |
|  4 | kangkang |
+----+-----------------+
3 rows in set (0.00 sec)
4>    指定条件查询
mysql> select id,name from student where name='oldsuo' and id=2;
+----+--------------+
| id | name   |
+----+---------------+
|  2 | oldsuo  |
+----+----------------+
1 row in set (0.00 sec)


mysql> select id,name from student where name='oldsuo' or id=3;
+----+----------+
| id | name     |
+----+----------+
|  2 | oldsuo   |
|  3 | kangknag |
+----+----------+
2 rows in set (0.03 sec)
    #升序
mysql> select id,name from student order by id asc;
+----+----------+
| id | name     |
+----+----------+
|  2 | oldsuo   |
|  3 | kangknag |
|  4 | kangkang |
+----+----------+
3 rows in set (0.00 sec)
    #倒叙
mysql> select id,name from student order by id desc;
+----+----------+
| id | name     |
+----+----------+
|  4 | kangkang |
|  3 | kangknag |
|  2 | oldsuo   |
+----+----------+
3 rows in set (0.00 sec)
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1>    插入单个数据，student为表的名称。
mysql> insert into student(id,name) values(1,'nick');
Query OK, 1 row affected (0.02 sec)
mysql> select * from student;
+----+--------------+------+--------+
| id | name   | age | dept |
+----+--------------+------+--------+
|  1 | nick |   0 | NULL |
+----+--------------+------+---------+
1 row in set (0.00 sec)
3>    批量插入数据，student为表的名称。
mysql> INSERT INTO  student(id,name) values(2,'oldsuo'),(3,'kangknag'),(4,'kangkang');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0
mysql> select * from student;
+----+-----------------+------+------+
| id | name     | age | dept |
+----+-----------------+------+------+
|  1 | nick   |  0 | NULL |
|  2 | oldsuo   |  0 | NULL |
|  3 | kangknag |  0 | NULL |
|  4 | kangknag |  0 | NULL |
+----+-----------------+------+--------+
3 rows in set (0.00 sec)
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1>    删除所有数据，student为表的名称。
mysql> delete from student;
Query OK, 8 rows affected (0.01 sec)
mysql> select * from student;
Empty set (0.00 sec)
2>    删除表中的某行或某些
mysql> delete from student where id=4;
Query OK, 1 row affected (0.00 sec)
mysql> delete from student where id>2;
Query OK, 1 row affected (0.00 sec)
mysql> delete from student where name='oldsuo';
Query OK, 1 row affected (0.00 sec)


3>    直接清空某张表
mysql> truncate table student;
Query OK, 0 rows affected (0.00 sec)
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mysql> use nick_defailt
Database changed
mysql> create table student (
      id int(4) not null,
      name char(20) not null,
      age tinyint(2) NOT NULL default '0',
      dept varchar(16) default NULL
      );
Query OK, 0 rows affected (0.05 sec)
mysql> show create table student\G        #查看建表语句
*************************** 1. row ***************************
       Table: student
Create Table: CREATE TABLE `student` (      #CREATE TABLE创建表的固定关键字，student为表名。
  `id` int(4) NOT NULL,                     #学号列，数字类型，长度为4，不为空值。
  `name` char(20) NOT NULL,                 #名字列，定长字符类型，长度20，不为空值。
  `age` tinyint(2) NOT NULL DEFAULT '0',    #年龄列，很小的数字类型，长度为2不为空，默认0。
  `dept` varchar(16) DEFAULT NULL           #系别列，变长字符类型，长度16，默认为空。
) ENGINE=MyISAM DEFAULT CHARSET=latin1      #引擎和字符集，引擎默认InnoDB，字符集lantin1。
1 row in set (0.00 sec)
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mysql> desc student;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(4)      | NO   |     | NULL    |       |
| name  | char(20)    | NO   |     | NULL    |       |
| age   | tinyint(2)  | NO   |     | 0       |       |
| dept  | varchar(16) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.04 sec)
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mysql> explain select * from student where name ='student' \G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: student
         type: ref　　　　　#有
possible_keys: index_name
          key: index_name  #表示有,详细见下文
       key_len: 20
          ref: const
         rows: 1           #检索了几行
        Extra: Using where
1 row in set (0.00 sec)
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MySQL提供了两个函数:


          from_unixtime(time_stamp)   ->  将时间戳转换为日期


          unix_timestamp(date)        ->  将指定的日期或者日期字符串转换为时间戳


SELECT from_unixtime(duedate/1000) duedate FROM organ WHERE refer='suoning';
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