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HomeDatabaseMysql Tutorial【数据库】SQLite与SQL差异问题汇总

【数据库】SQLite与SQL差异问题汇总

Jun 07, 2016 pm 03:10 PM
sqlsqlitedifferencedatabaseSummaryquestion

编者注:这些关于SQLite与SQL差异的问题,你是否遇到过呢?笔者在这里为大家总结出了使用SQLite时,与SQL之间经常会出现的一些差异性问题,希望对大家的使用有所帮助。 一、常见问题汇总 1 TOP 这是一个大家经常问到的问题,例如在SQLSERVER中可以使用如下语

编者注:这些关于SQLite与SQL差异的问题,你是否遇到过呢?笔者在这里为大家总结出了使用SQLite时,与SQL之间经常会出现的一些差异性问题,希望对大家的使用有所帮助。

一、常见问题汇总

1 TOP

这是一个大家经常问到的问题,例如在SQLSERVER中可以使用如下语句来取得记录集中的前十条记录:

<ol><li><span><span>SELECT</span><span> </span><span>TOP</span><span> 10 * </span><span>FROM</span><span> [</span><span>index</span><span>] </span><span>ORDER</span><span> </span><span>BY</span><span> indexid </span><span>DESC</span><span>; </span></span></li></ol>

但是这条SQL语句在SQLite中是无法执行的,应该改为:

<ol><li><span><span>SELECT</span><span> * </span><span>FROM</span><span> [</span><span>index</span><span>] </span><span>ORDER</span><span> </span><span>BY</span><span> indexid </span><span>DESC</span><span> limit 0,10; </span></span></li></ol>

其中limit 0,10表示从第0条记录开始,往后一共读取10条

2 创建视图(Create View)

SQLite在创建多表视图的时候有一个BUG,问题如下:

<ol><li><span><span>CREATE</span><span> </span><span>VIEW</span><span> watch_single </span><span>AS</span><span> </span><span>SELECT</span><span> DISTINCTwatch_item.[watchid],watch_item.[itemid] </span><span>FROM</span><span> watch_item; </span></span></li></ol>

上面这条SQL语句执行后会显示成功,但是实际上除了

<ol><li><span><span>SELECT</span><span> </span><span>COUNT</span><span>(*) </span><span>FROM</span><span> [watch_single ] </span><span>WHERE</span><span> watch_ single.watchid = 1; </span></span></li></ol>

能执行之外是无法执行其他任何语句的。其原因在于建立视图的时候指定了字段所在的表名,而SQLite并不能正确地识别它。所以上面的创建语句要改为:

<ol><li><span><span>CREATE</span><span> </span><span>VIEW</span><span> watch_single </span><span>AS</span><span> </span><span>SELECT</span><span> </span><span>DISTINCT</span><span> [watchid],[itemid] </span><span>FROM</span><span> watch_item; </span></span></li></ol>

但是随之而来的问题是如果是多表的视图,且表间有重名字段的时候该怎么办?

3 COUNT(DISTINCT column)

SQLite在执行如下语句的时候会报错:

<ol><li><span><span>SELECT</span><span> </span><span>COUNT</span><span>(</span><span>DISTINCT</span><span> watchid) </span><span>FROM</span><span> [watch_item] </span><span>WHERE</span><span> watch_item.watchid = 1; </span></span></li></ol>

其原因是SQLite的所有内置函数都不支持DISTINCT限定,所以如果要统计不重复的记录数的时候会出现一些麻烦。比较可行的做法是先建立一个不重复的记录表的视图,然后再对该视图进行计数。

4 外连接

虽然SQLite官方已经声称LEFT OUTER JOIN 已经实现,但还没有 RIGHT OUTER JOIN 和 FULL OUTER JOIN。但是实际测试表明似乎并不能够正常的工作。以下三条语句在执行的时候均会报错:

<ol>
<li><span><span>SELECT</span><span> tags.[tagid] </span><span>FROM</span><span> [tags],[tag_rss] </span><span>WHERE</span><span> tags.[tagid] = tag_rss.[tagid](*);  </span></span></li>
<li>
<span>SELECT</span><span> tags.[tagid] </span><span>FROM</span><span> [tags],[tag_rss] </span><span>WHERE</span><span> </span><span>LEFT</span><span> </span><span>OUTER</span><span> </span><span>JOIN</span><span> tag_rss.[tagid] = tags.[tagid];  </span>
</li>
<li>
<span>SELECT</span><span> tags.[tagid] </span><span>FROM</span><span> [tags],[tag_rss] </span><span>WHERE</span><span> </span><span>LEFT</span><span> </span><span>JOIN</span><span> tag_rss.[tagid] = tags.[tagid]; </span>
</li>
</ol>

此外经过测试用+号代替*号也是不可行的。

二、收集SQLite与Sql Server的语法差异

1.返回最后插入的标识值

返回最后插入的标识值sql server用@@IDENTITY

sqlite用标量函数LAST_INSERT_ROWID()

返回通过当前的 SQLConnection 插入到数据库的最后一行的行标识符(生成的主键)。此值与 SQLConnection.lastInsertRowID 属性返回的值相同。

2.top n

在sql server中返回前2行可以这样:

<ol>
<li><span><span>select</span><span> </span><span>top</span><span> 2 * </span><span>from</span><span> aa   </span></span></li>
<li>
<span>order</span><span> </span><span>by</span><span> ids </span><span>desc</span><span> </span>
</li>
</ol>

sqlite中用LIMIT,语句如下:

<ol>
<li><span><span>select</span><span> * </span><span>from</span><span> aa   </span></span></li>
<li>
<span>order</span><span> </span><span>by</span><span> ids </span><span>desc</span><span>   </span>
</li>
<li><span>LIMIT 2 </span></li>
</ol>

3.GETDATE ( )

在sql server中GETDATE ( )返回当前系统日期和时间

sqlite中没有

4.EXISTS语句

sql server中判断插入(不存在ids=5的就插入)

<ol>
<li><span><span>IF </span><span>NOT</span><span> EXISTS (</span><span>select</span><span> * </span><span>from</span><span> aa </span><span>where</span><span> ids=5)   </span></span></li>
<li>
<span>BEGIN</span><span>   </span>
</li>
<li>
<span>insert</span><span> </span><span>into</span><span> aa(nickname)   </span>
</li>
<li>
<span>select</span><span> </span><span>'t'</span><span>   </span>
</li>
<li>
<span>END</span><span>   </span>
</li>
</ol>

在sqlite中可以这样

<ol>
<li><span><span>insert</span><span> </span><span>into</span><span> aa(nickname)   </span></span></li>
<li>
<span>select</span><span> </span><span>'t'</span><span>   </span>
</li>
<li>
<span>where</span><span> </span><span>not</span><span> exists(</span><span>select</span><span> * </span><span>from</span><span> aa </span><span>where</span><span> ids=5) </span>
</li>
</ol>

5.嵌套事务

sqlite仅允许单个活动的事务

6.RIGHT 和 FULL OUTER JOIN

sqlite不支持 RIGHT OUTER JOIN 或 FULL OUTER JOIN

7.可更新的视图

sqlite视图是只读的。不能对视图执行 DELETE、INSERT 或 UPDATE 语句,sql server是可以对视图 DELETE、INSERT 或 UPDATE

三、新增内容

1.关于日期时间类型列的默认设置:

对"列"的设置包括三个字段:Name、Type、Default

Name:logTime(随意命名);

Type:

Date类型,得到的值形如"2011-04-23",

DATETIME类型,得到的值形如"2011-04-23 11:49:04.000";

Default:datetime('now','localtime')  我采用的是两个参数,后面的localtime不要丢弃,不然时间不准确。

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