BlogJava-LoveJava-LoveLife-随笔分类-oraclehttp://www.blogjava.net/michaellee/category/40704.html再烦，也别忘微笑；再急，也要注意语气；再苦，也别忘坚持；再累，也要爱自己 zh-cnMon, 21 Dec 2009 22:12:02 GMTMon, 21 Dec 2009 22:12:02 GMT60数据库查询优化方案（处理上百万级记录如何提高处理查询速度） http://www.blogjava.net/michaellee/archive/2009/12/19/306666.htmlMichaelLeeMichaelLeeSat, 19 Dec 2009 07:23:00 GMThttp://www.blogjava.net/michaellee/archive/2009/12/19/306666.htmlhttp://www.blogjava.net/michaellee/comments/306666.htmlhttp://www.blogjava.net/michaellee/archive/2009/12/19/306666.html#Feedback0http://www.blogjava.net/michaellee/comments/commentRss/306666.htmlhttp://www.blogjava.net/michaellee/services/trackbacks/306666.html2.应尽量避免在 where 子句中对字段进行 null 值判断，否则将导致引擎放弃使用索引而进行全表扫描，如：
select id from t where num is null
可以在num上设置默认值0，确保表中num列没有null值，然后这样查询：
select id from t where num=0  阅读全文

MichaelLee 2009-12-19 15:23 发表评论
]]>sql语法/用法整理（修正版）http://www.blogjava.net/michaellee/archive/2009/11/23/303354.htmlMichaelLeeMichaelLeeMon, 23 Nov 2009 08:10:00 GMThttp://www.blogjava.net/michaellee/archive/2009/11/23/303354.htmlhttp://www.blogjava.net/michaellee/comments/303354.htmlhttp://www.blogjava.net/michaellee/archive/2009/11/23/303354.html#Feedback0http://www.blogjava.net/michaellee/comments/commentRss/303354.htmlhttp://www.blogjava.net/michaellee/services/trackbacks/303354.html
分组group

　　常用于统计时，如分组查总数：
select gender,count(sno)
from students
group by gender
(查看男女学生各有多少)

　　注意：从哪种角度分组就从哪列"group by"  阅读全文

MichaelLee 2009-11-23 16:10 发表评论
]]>SQL语句 SELECT LIKE like用法详解http://www.blogjava.net/michaellee/archive/2009/11/23/303353.htmlMichaelLeeMichaelLeeMon, 23 Nov 2009 08:06:00 GMThttp://www.blogjava.net/michaellee/archive/2009/11/23/303353.htmlhttp://www.blogjava.net/michaellee/comments/303353.htmlhttp://www.blogjava.net/michaellee/archive/2009/11/23/303353.html#Feedback0http://www.blogjava.net/michaellee/comments/commentRss/303353.htmlhttp://www.blogjava.net/michaellee/services/trackbacks/303353.html阅读全文

MichaelLee 2009-11-23 16:06 发表评论
]]>SQL PRIMARY KEY 约束http://www.blogjava.net/michaellee/archive/2009/11/23/303348.htmlMichaelLeeMichaelLeeMon, 23 Nov 2009 07:35:00 GMThttp://www.blogjava.net/michaellee/archive/2009/11/23/303348.htmlhttp://www.blogjava.net/michaellee/comments/303348.htmlhttp://www.blogjava.net/michaellee/archive/2009/11/23/303348.html#Feedback0http://www.blogjava.net/michaellee/comments/commentRss/303348.htmlhttp://www.blogjava.net/michaellee/services/trackbacks/303348.html
主键必须包含唯一的值。

主键列不能包含 NULL 值。

每个表应该都一个主键，并且每个表只能有一个主键。
SQL PRIMARY KEY Constraint on CREATE TABLE  阅读全文

MichaelLee 2009-11-23 15:35 发表评论
]]>oracle怎么实现左联，右联与外联?9i以前写法 9i以后10g 11g的写法http://www.blogjava.net/michaellee/archive/2009/07/08/285907.htmlMichaelLeeMichaelLeeWed, 08 Jul 2009 02:19:00 GMThttp://www.blogjava.net/michaellee/archive/2009/07/08/285907.htmlhttp://www.blogjava.net/michaellee/comments/285907.htmlhttp://www.blogjava.net/michaellee/archive/2009/07/08/285907.html#Feedback0http://www.blogjava.net/michaellee/comments/commentRss/285907.htmlhttp://www.blogjava.net/michaellee/services/trackbacks/285907.html select a.id,a.name,b.address from a,b
where a.id=b.id(+)
右联:
select a.id,a.name,b.address from a,b
where a.id(+)=b.id
外联
SELECT a.id,a.name,b.address
FROM a,b
WHERE a.id = b.id(+)
UNION

SELECT b.id,'' name,b.address
FROM b
WHERE NOT EXISTS (
SELECT * FROM a
WHERE a.id = b.id);
在9i以上，已经开始支持SQL99标准，所以，以上语句可以写成：
默认内部联结：
select a.id,a.name,b.address,c.subject
from (a inner join b on a.id=b.id)
inner join c on b.name = c.name
where other_clause
左联
select a.id,a.name,b.address
from a left outer join b on a.id=b.id
where other_clause
右联
select a.id,a.name,b.address
from a right outer join b on a.id=b.id
where other_clause
外联
select a.id,a.name,b.address
from a full outer join b on a.id=b.id
where other_clause
or
select a.id,a.name,b.address
from a full outer join b using (id)
where other_clause


MichaelLee 2009-07-08 10:19 发表评论
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