SQL必知必会 14-22（完）

博主依然不想打字，又向你仍来了一堆代码。。。

13（续）

在SELECT中用COUNT（）以及联合

mysql> SELECT customers.cust_id,COUNT(orders.order_num) AS num_ord

    -> FROM customers INNER JOIN orders

    ->  ON customers.cust_id=orders.cust_id

    -> GROUP BY cust_id;

+------------+---------+

| cust_id    | num_ord |

+------------+---------+

| 1000000001 |       2 |

| 1000000003 |       1 |

| 1000000004 |       1 |

| 1000000005 |       1 |

+------------+---------+

4 rows in set (0.00 sec)

14、组合查询

UNION，UNION ALL（显示重复行）；

多条SELECT合并为一个查询输出；

必须有相同的列数，顺序可以不一样但数据类型要可以转换的；

UNION ALL显示重复行，除此以外的使用，都可以用WHERE来替换；

ORDER BY放在最后一句，只需要一句；

不过事实证明，顺序还是会有影响的。。。

mysql> SELECT cust_name,cust_contact,cust_emali

    -> FROM customers

    -> WHERE cust_state IN ('IL','IN','MI');

ERROR 1054 (42S22): Unknown column 'cust_emali' in 'field list'

mysql> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_state IN ('IL','IN','MI');

+---------------+--------------+-----------------------+

| cust_name     | cust_contact | cust_email            |

+---------------+--------------+-----------------------+

| Village Toys  | John Smith   | sales@villagetoys.com |

| Fun4All       | Jim Jones    | jjones@fun4all.com    |

| The Toy Store | Kim Howard   | NULL                  |

+---------------+--------------+-----------------------+

3 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_email,cust_contact

    -> FROM customers

    -> WHERE cust_name='Fun4All';

+-----------+-----------------------+--------------------+

| cust_name | cust_email            | cust_contact       |

+-----------+-----------------------+--------------------+

| Fun4All   | jjones@fun4all.com    | Jim Jones          |

| Fun4All   | dstephens@fun4all.com | Denise L. Stephens |

+-----------+-----------------------+--------------------+

2 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_state IN ('IL','IN','MI')

    -> UNION

    -> SELECT cust_name,cust_email,cust_contact

    -> FROM customers

    -> WHERE cust_name='Fun4All';

+---------------+-----------------------+-----------------------+

| cust_name     | cust_contact          | cust_email            |

+---------------+-----------------------+-----------------------+

| Village Toys  | John Smith            | sales@villagetoys.com |

| Fun4All       | Jim Jones             | jjones@fun4all.com    |

| The Toy Store | Kim Howard            | NULL                  |

| Fun4All       | jjones@fun4all.com    | Jim Jones             |

| Fun4All       | dstephens@fun4all.com | Denise L. Stephens    |

+---------------+-----------------------+-----------------------+

5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_state IN ('IL','IN','MI')

    -> UNION

    -> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_name='Fun4All';

+---------------+--------------------+-----------------------+

| cust_name     | cust_contact       | cust_email            |

+---------------+--------------------+-----------------------+

| Village Toys  | John Smith         | sales@villagetoys.com |

| Fun4All       | Jim Jones          | jjones@fun4all.com    |

| The Toy Store | Kim Howard         | NULL                  |

| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |

+---------------+--------------------+-----------------------+

4 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_state IN ('IL','IN','MI')

    -> UNION ALL

    -> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_name='Fun4All';

+---------------+--------------------+-----------------------+

| cust_name     | cust_contact       | cust_email            |

+---------------+--------------------+-----------------------+

| Village Toys  | John Smith         | sales@villagetoys.com |

| Fun4All       | Jim Jones          | jjones@fun4all.com    |

| The Toy Store | Kim Howard         | NULL                  |

| Fun4All       | Jim Jones          | jjones@fun4all.com    |

| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |

+---------------+--------------------+-----------------------+

5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_state IN ('IL','IN','MI')

    -> UNION

    -> SELECT cust_name,cust_contact,cust_email

    -> FROM customers

    -> WHERE cust_name='Fun4All'

    -> ORDER BY cust_name;

+---------------+--------------------+-----------------------+

| cust_name     | cust_contact       | cust_email            |

+---------------+--------------------+-----------------------+

| Fun4All       | Jim Jones          | jjones@fun4all.com    |

| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |

| The Toy Store | Kim Howard         | NULL                  |

| Village Toys  | John Smith         | sales@villagetoys.com |

+---------------+--------------------+-----------------------+

4 rows in set (0.00 sec)

15、插入数据

INSERT,INSERT INTO,INSERT SELECT,SELECT INTO

插入完整的行，插入行的一部分，插入某些查询结果；

用INSERT INTO替代INSERT，提高可移植性；

注意格式写法；

最好写上列名；

INSERT一般只能插入一条，INSERT SELECT是个例外；

SELECT INTO实现复制（MySQL和Oracle的有所不同）

mysql> CREATE TABLE custNew(

    -> cust_id INT PRIMARY KEY,

    -> cust_contact VARCHAR(32),

    -> cust_email VARCHAR(32),

    -> cust_name VARCHAR(32),

    -> cust_address VARCHAR(64),

    -> cust_city VARCHAR(16),

    -> cust_state VARCHAR(16),

    -> cust_zip SMALLINT,

    -> cust_country VARCHAR(16)

    -> );

Query OK, 0 rows affected (0.21 sec)

mysql> INSERT INTO custNew(

    ->   cust_id,

    ->   cust_email,

    ->   cust_name,

    ->   cust_zip,

    ->   cust_country,

    ->   cust_city)

    -> VALUES(

    ->   1021,

    ->   'liangbocv@126.com',

    ->   'Andy Liang',

    ->   610000,

    ->   'China',

    ->   'Chengdu');

Query OK, 1 row affected, 1 warning (0.04 sec)

mysql> INSERT INTO customers(

    ->   cust_id,

    ->   cust_email,

    ->   cust_name,

    ->   cust_zip,

    ->   cust_country,

    ->   cust_city)

    -> SELECT cust_id,

    ->   cust_email,

    ->   cust_name,

    ->   cust_zip,

    ->   cust_country,

    ->   cust_city

    -> FROM custNew;

Query OK, 1 row affected (0.03 sec)

Records: 1  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM customers;

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |

| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |

| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |

| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |

| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |

| 1021       | Andy Liang    | NULL                 | Chengdu   | NULL       | 32767    | China        | NULL               | liangbocv@126.com     |

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

6 rows in set (0.00 sec)

mysql> CREATE TABLE custcopy(

    -> cust_id VARCHAR(16),

    -> cust_contact VARCHAR(32),

    -> cust_email VARCHAR(32),

    -> cust_name VARCHAR(32),

    -> cust_address VARCHAR(64),

    -> cust_city VARCHAR(16),

    -> cust_state VARCHAR(16),

    -> cust_zip VARCHAR(16),

    -> cust_country VARCHAR(16)

    -> );

Query OK, 0 rows affected (0.26 sec)

mysql> SELECT *

    -> INTO custcopy

    -> FROM customers;

ERROR 1327 (42000): Undeclared variable: custcopy

mysql> CREATE TABLE custcopy2 AS

    -> SELECT *

    -> FROM customers;

Query OK, 6 rows affected (0.41 sec)

Records: 6  Duplicates: 0  Warnings: 0

16、更新和删除数据

UPADTE,DELETE

容易使用，但请小心使用；（没有UNDO！！！）

UPDATE为null=DELETE；

一些习惯：一定带WHERE ,避免对整个表有影响；

对数据做更改时，请先SELECT查询一下，看对象是否没错；

确保每个表有主键

mysql> SELECT cust_id,cust_address,cust_state

    -> FROM customers

    -> WHERE cust_id='';

+---------+--------------+------------+

| cust_id | cust_address | cust_state |

+---------+--------------+------------+

| 1021    | NULL         | NULL       |

+---------+--------------+------------+

1 row in set (0.00 sec)

mysql> UPDATE customers

    -> SET cust_address='2006 Xiyuan Ave.',

    ->     cust_state='SC'

    -> WHERE cust_id='';

Query OK, 1 row affected (0.02 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT cust_id,cust_address,cust_state

    -> FROM customers

    -> WHERE cust_id='';

+---------+------------------+------------+

| cust_id | cust_address     | cust_state |

+---------+------------------+------------+

| 1021    | 2006 Xiyuan Ave. | SC         |

+---------+------------------+------------+

1 row in set (0.00 sec)

mysql> UPDATE customers

    -> SET cust_email=NULL

    -> WHERE cust_id='';

Query OK, 1 row affected (0.03 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> DELETE FROM customers

    -> WHERE cust_id='';

Query OK, 1 row affected (0.08 sec)

17、创建和操作表

CREATE,DROP,ALTER,RENAME,DEFAULT

更新表，和更新数据一样小心，做好备份；

重命名不太一样，mysql是RENAME

mysql> ALTER TABLE custcopy2

    -> ADD cust_gender VARCHAR(8);

Query OK, 0 rows affected (0.41 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> SELECT CURRENT_DATE();

+----------------+

| CURRENT_DATE() |

+----------------+

| 2016-08-10     |

+----------------+

1 row in set (0.16 sec)

mysql> ALTER TABLE custcopy2

    -> ADD add_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP;

Query OK, 0 rows affected (0.46 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> DROP TABLE custcopy;

Query OK, 0 rows affected (0.13 sec)

mysql> RENAME TABLE custcopy2 TO custcopy;

Query OK, 0 rows affected (0.10 sec)

18、使用视图

VIEW

view实际上就是个虚拟的表，只包含使用时动态检索数据的查询；

使用view，有利于代码重用，保护数据，简化操作；

视图名也要唯一；可以嵌套，一般禁止ORDER BY；

用于简化复杂联结，格式化输出，过滤不想要的数据等；

WHERE语句会自动合并

mysql> CREATE VIEW shit AS

    -> SELECT cust_name,cust_id,cust_contact,cust_address

    -> FROM customers

    -> ;

Query OK, 0 rows affected (0.07 sec)

mysql> SELECT cust_name,cust_address

    -> FROM shit

    -> WHERE cust_id='';

Empty set (0.00 sec)

mysql> SELECT * FROM customers;

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |

| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |

| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |

| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |

| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_address

    -> FROM shit

    -> WHERE cust_id='';

+--------------+----------------+

| cust_name    | cust_address   |

+--------------+----------------+

| Village Toys | 200 Maple Lane |

+--------------+----------------+

1 row in set (0.00 sec)

mysql> CREATE VIEW hasEmail AS

    -> SELECT cust_name,cust_id,cust_email

    -> FROM customers

    -> WHERE cust_email IS NOT NULL;

Query OK, 0 rows affected (0.06 sec)

mysql> SELECT *

    -> FROM hasEmail

    -> WHERE cust_name='Fun4All';

+-----------+------------+-----------------------+

| cust_name | cust_id    | cust_email            |

+-----------+------------+-----------------------+

| Fun4All   | 1000000003 | jjones@fun4all.com    |

| Fun4All   | 1000000004 | dstephens@fun4all.com |

+-----------+------------+-----------------------+

2 rows in set (0.00 sec)

19、存储过程

PROCEDURE,DELIMITER,CALL

以下引用自百度：存储过程（Stored Procedure）是在大型数据库系统中，一组为了完成特定功能的SQL 语句集，存储在数据库中，经过第一次编译后再次调用不需要再次编译，用户通过指定存储过程的名字并给出参数（如果该存储过程带有参数）来执行它。存储过程是数据库中的一个重要对象，任何一个设计良好的数据库应用程序都应该用到存储过程。

有点好玩又有点繁琐的。。。

mysql> DELIMITER &&

mysql> CREATE PROCEDURE showAll()

    ->   BEGIN

    ->   SELECT * FROM customers;

    -> END &&

Query OK, 0 rows affected (0.04 sec)

mysql> CALL showAll();

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |

| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |

| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |

| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |

| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |

+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+

5 rows in set (0.00 sec)

Query OK, 0 rows affected (0.08 sec)

mysql> DELIMITER $

mysql> CREATE PROCEDURE getID(

    ->   IN id VARCHAR(32))

    ->   BEGIN

    ->   SELECT *

    ->   FROM customers

    ->   WHERE cust_id=id;

    -> END $

Query OK, 0 rows affected (0.00 sec)

mysql> CALL getID('')$

+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+

| cust_id    | cust_name    | cust_address   | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email            |

+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+

| 1000000001 | Village Toys | 200 Maple Lane | Detroit   | MI         | 44444    | USA          | John Smith   | sales@villagetoys.com |

+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+

1 row in set (0.00 sec)

Query OK, 0 rows affected (0.03 sec)

mysql> DELIMITER ;

注意输入参数那里的变化。

20、事务管理

TRANSACTION,COMMIT,ROLLBACK,SAVEPOINT

用来维护数据库的完整性，保证成批的SQL操作要么完全执行，要么完全不执行；

保留点越多越好，更好的是形成习惯~

mysql> BEGIN;

Query OK, 0 rows affected (0.00 sec)

mysql> SAVEPOINT begin;

Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO customers(cust_name,cust_country)

    ->  VALUES('Andy Liang','China');

Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> ROLLBACK TO begin;

Query OK, 0 rows affected (0.04 sec)

mysql> COMMIT;

Query OK, 0 rows affected (0.00 sec)

MySQL是一步步来的，就是慢慢监督的一样。

21、使用游标

CURSOR

略。。。。（老子做web不想用游标，你来打我啊

22、约束，索引，触发器

约束:

PRIMARY KEY,UNIQUE,REFERENCES,ALTER,CONSTRAINT,CHECK

主键：值互异，NOT NULL，不修改/更新，不重用，每个表仅能有一个主键，可以用来定义外键（举例：id

唯一：值互异，可以有NULL，可修改/更新，可重用，可有多个唯一键，不能用来定义外键

外键：两个表，确定子表某一列的合法性

检查约束：CHECK，灵活约束

mysql> CREATE TABLE test(

    -> id SMALLINT NOT NULL PRIMARY KEY AUTO_INCREMENT,

    -> socialid VARCHAR(64) UNIQUE,

    -> cust_id VARCHAR(16) NOT NULL REFERENCES customers(cust_id),

    -> quantity SMALLINT CHECK (quantity>0),

    -> gender VARCHAR(8) CHECK (gender LIKE '[MF]')

    -> );

Query OK, 0 rows affected (0.20 sec)

另外，用ALTER语句再对表进行更改操作

ALTER TABLE test

ADD CONSTRAINT PRIMARY KEY (cust_id);

ALTER TABLE test

ADD CONSTRAINT UNIQUE KEY (id);

ALTER TABLE test

ADD CONSTRAINT

FOREIGN KEY (cust_id) REFERENCES customers (cust_id);

ALTER TABLE test

ADD CONSTRAINT CHECK (quantity<1000);

索引：

INDEX

搜索某些列的效率提高；

请动态的创建索引——数据库在不断更新，索引效率在变化；索引效率提升的代价是插入等操作性能的牺牲；大量空间的使用；

mysql> CREATE INDEX prod_name_id

    -> ON PRODUCTS (prod_name);

Query OK, 0 rows affected (0.31 sec)

Records: 0  Duplicates: 0  Warnings: 0

触发器：

TRIGGER

在特定的数据库活动发生时自动执行；

一般用途：保证数据一致（全大写等），联动（log的记录）等；

约束要比触发器快，尽量用约束；

完！！（对，这里又灭有代码了

SQL必知必会 14-22（完）的更多相关文章

你必知必会的SQL面试题
写在前面的话本文参考原博<走向面试之数据库基础:一.你必知必会的SQL语句练习-Part 1>和<走向面试之数据库基础:一.你必知必会的SQL语句练习-Part 2>进行练习 ...
SQL 必知必会
本文介绍基本的 SQL 语句,包括查询.过滤.排序.分组.联结.视图.插入数据.创建操纵表等.入门系列,不足颇多,望诸君指点. 注意本文某些例子只能在特定的DBMS中实现(有的已标明,有的未标明),不 ...
读书笔记--SQL必知必会--建立练习环境
书目信息中文名:<SQL必知必会(第4版)> 英文名:<Sams Teach Yourself SQL in 10 Minutes - Fourth Edition> MyS ...
0005 《SQL必知必会》笔记01-SELECT语句
1.SELECT基本语句: SELECT 字段名1,···,字段名n FROM 表名 2.检索所有字段,用"*"替换字段名,这会导致效率低下 SELECT * FROM 表名; 3 ...
《SQL必知必会》学习笔记二)
<SQL必知必会>学习笔记(二) 咱们接着上一篇的内容继续.这一篇主要回顾子查询,联合查询,复制表这三类内容. 上一部分基本上都是简单的Select查询,即从单个数据库表中检索数据的单条语 ...
MySQL必知必会-官方数据库表及SQL脚本导入生成
最近在复习SQL语句,看的是MySQL必知必会这本书,但是发现附录中只有表设计,没有表的具体数据.所以在学习相应的语句中体验不是很好,去网上查了数据库的内容,自己慢慢导入到了数据库中.把表放出来作为参 ...
《SQL必知必会》学习笔记整理
简介本笔记目前已包含 <SQL必知必会>中的所有章节. 我在整理笔记时所考虑的是:在笔记记完后,当我需要查找某个知识点时,不需要到书中去找,只需查看笔记即可找到相关知识点.因此在整理笔记 ...
读书笔记汇总 - SQL必知必会（第4版）
本系列记录并分享学习SQL的过程,主要内容为SQL的基础概念及练习过程. 书目信息中文名:<SQL必知必会(第4版)> 英文名:<Sams Teach Yourself SQL i ...
读书笔记--SQL必知必会12--联结表
12.1 联结联结(join),利用SQL的SELECT在数据查询的执行中联结表. 12.1.1 关系表关系数据库中,关系表的设计是把信息分解成多个表,一类数据一个表,各表通过某些共同的值互相关联 ...
读书笔记--SQL必知必会18--视图
读书笔记--SQL必知必会18--视图 18.1 视图视图是虚拟的表,只包含使用时动态检索数据的查询. 也就是说作为视图,它不包含任何列和数据,包含的是一个查询. 18.1.1 为什么使用视图重用 ...

随机推荐

NodeJs+Request+Cheerio 采集数据
目的:采集网站文章. 两个依赖项: request :https://github.com/request/request cheerio:https://github.com/cheeriojs/c ...
Bootstrap WPF Style,Bootstrap风格的WPF样式
简介 GitHub地址:https://github.com/ptddqr/bootstrap-wpf-style 此样式基于bootstrap-3.3.0,样式文件里的源码行数都是指的这个版本.CS ...
设计模式(十三)：从“FQ”中来认识代理模式(Proxy Pattern)
我们知道Google早就被墙了,所以FQ才能访问Google呢,这个“FQ”的过程就是一个代理的过程.“代理模式”在之前的博客中不止一次的提及过,之前的委托回调就是代理模式的具体应用.今天我们就从“F ...
探寻<a>中的href和onclick
一.知识点: onclick的方法参数必须加引号 href跳转参数有长度限制 href中执行js会把encodeURIComponent()编码之后的东西自动解码,有时会影响参数传递 a标签中的onc ...
Events基本概念----Beginning Visual C#
span.kw { color: #007020; font-weight: bold; } code > span.dt { color: #902000; } code > span. ...
Python（七）Socket编程、IO多路复用、SocketServer
本章内容: Socket IO多路复用(select) SocketServer 模块(ThreadingTCPServer源码剖析) Socket socket通常也称作"套接字" ...
JavaScript学习（一） —— 环境搭建与JavaScript初探
1.开发环境搭建本系列教程的开发工具,我们采用HBuilder. 可以去网上下载最新的版本,然后解压一下就能直接用了.学习JavaScript,环境搭建是非常简单的,或者说,只要你有一个浏览器,一个 ...
利用Python进行数据分析(11) pandas基础: 层次化索引
层次化索引层次化索引指你能在一个数组上拥有多个索引,例如: 有点像Excel里的合并单元格对么? 根据索引选择数据子集以外层索引的方式选择数据子集: 以内层索引的方式选择数据: 多重索引S ...
sql 补齐字段位数
select top 100 lmdte, right(replicate('0',6)+ltrim(lmtme),6) from smtpdsum where lmdte <> 0
[C#项目开源] MongoDB 可视化管理工具 (2011年10月-至今)
正文该项目从2011年10月开始开发,知道现在已经有整整5年了.MongoDB也从一开始的大红大紫到现在趋于平淡. MongoCola这个工具在一开始定位的时候只是一个Windows版本的工具,期间 ...

SQL必知必会 14-22（完）

SQL必知必会 14-22（完）的更多相关文章

随机推荐

热门专题