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数据库基本操作小摘（代码由mysql-essential-5.1.50-win32测试通过）

2010-08-24 22:45 841 查看

[此文于2010年8月22日被重新编辑]

本篇所有的内容都为本人在学习SQL中的学习札记，其中参考了《SQL Cookbook》与《SQL HACKS》这两本书，其余的资源来自于网络，通过学习后发现其实SQL中的很多技巧都是关键字的多种组合，所以了解关键字的用法才是重中之重。以下知识点只是起到一个摘抄作用，如果想了解更多详细的内容可以去查看这两本书，书中包含很多不同数据库的内置函数（本文没有涉及此方面），想要深入的学习只能多加应用才是。
[插入、更新与删除]
#创建数据库：CREATE DATABASE menagerie
#插入默认值：CREATE TABLE D(id integer default 0)
#查看当前状态： STATUS
#切换字符集：SET character_set_connection=gb2312 （参考更多：http://chenboqiang.blog.51cto.com/1068057/268639）

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.csharpcode .lnum { color: #606060; } #从一个表向另外的表中复制行：

1:  INSERT INTO dept1（deptno,dname,loc）

2:   SELECT deptno,dname,loc

3:     FROM dep2

4:     WHERE loc IN(‘New’,‘BOS’,)

1:  CREATE TABLE dept_2

2:  AS

3:  SELECT *

4:     FROM dept

5:     WHERE 1=0

#一次向多个表插入记录：目前(2007.10.1)Oracle和DB2支持

# 阻止对某列插入：

1:  CREATE VIEW new_emps as

2:  SELECT empno,ename,job

3:     FROM emp

1:  SELECT depno,

2:         ename,

3:         sal as orig_sal

4:         sal*.10 as new_sal

5:         FROM emp

6:         WHERE deptno=20

7:         ORDER BY 1,5

1:  UPDATE emp

2:     SET sal=sal*1.20

3:     WHERE empno in(SELECT empno FROM emp_bonus)

1:  UPDATE emp e SET (e.sla,e.comm)=(SELECT ns.sal,ns.sal/2

2:                                   FROM new_sal ns

3:                                   WHERE ns.deptno=e.deptno)

4:  WHERE EXISTS( SELECT NULL

5:                FROM  new_sal ns

6:                WHERE ns.deptno=e.deptno)

#合并记录：
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.csharpcode .asp { background-color: #ffff00; }
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1:  MERGE INTO emp_commission ec

2:  USING (SELECT * FROM emp) emp

3:     ON(ec.empno=emp.empno)

4:  WHEN matched THEN

5:     UPDATE SET ec.comm=1000

6:     DELETE WHRER(sal<2000)

7:  WHEN NOT matched THEN

8:     INSERT(ec.empno,ec.ename,ec.deptno,ec.coomm)

9:     VALUES(ec.empno,ec.ename,ec.deptno,ec.coomm)

1:   select concat(ename, ' WORKS AS A ',job) as msg

2:        from

3:        where deptno=10

1:   select *

2:         from emp limit 5

1:  select *

2:       from emp

3:       where comm is null

1:  1select ename, job

2:      from emp

3:      where deptno in (10,20)

4:      and (ename like '%I%' or job like '%ER')

1:   select ename,job,sal

2:       from emp

3:       where deptno = 10

4:       order by sal asc

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（ asc升序 desc降序，order by优先次序从左到右）

#按字串排序：substr或者substring函数

[操作多个表]

#记录集的叠加：UNION 操作符用于合并两个或多个 SELECT 语句的结果集。UNION 内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每条 SELECT 语句中的列的顺序必须相同。

#组合相关行：

1:  select e.ename, d.loc

2:        from emp e inner join dept d

3:          on (e.deptno = d.deptno)

4:       where e.deptno = 10

1:  select e.ename, e.deptno as emp_deptno, d.*

2:        from dept d left join emp e

3:          on (d.deptno = e.deptno)

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.csharpcode .rem { color: #008000; }
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[使用数字]

#平均值：avg

#最大最小值：max, min

#总和：sum

#行数：count(*)

#某列值非NULL的个数：count(comm)

#乘机：sum over

#计算不包含最大值和最小值的均值：

1:   select avg(sal)

2:       from emp

3:       where sal not in (

4:         (select min(sal) from emp),

5:         (select max(sal) from emp)

6:       )

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.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
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.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
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.csharpcode .lnum { color: #606060; }

未完待续……

参考文献：《SQL Cookbook》——清华大学出版社，Antbony Molinaro著，王强&王晓娟等译——ISBN 978-7-302-15493-8

《SQL HACKS》——清华大学出版社，Andrew Cumming&Gordon Russell著，张长富等译——ISBN 978-7-302-17484-4

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