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21.9.2 SQL Server的键生成
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21.9.2 SQL Server的键生成
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<link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><a ftel="_Toc507815174"><span lang="EN-GB">21.9.2 SQL Server</span></a><span style="FONT-FAMILY: 黑体">的键生成</span></h3>
<p class="MsoNormal"><a ftel="SQLServerkeys"><span style="FONT-FAMILY: 宋体">本章前面给出的</span><span lang="EN-US">RegionInsert</span></a><span style="FONT-FAMILY: 宋体">存储过程在给数据库插入数据时生成了一个主键码值。生成该键的方法相当原始，没有很好地考虑，真正的应用程序应利用生成键的其他策略。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">首先要定义一个</span><span lang="EN-US">Identity</span><span style="FONT-FAMILY: 宋体">列，从存储过程中返回</span><span lang="EN-US" style="FONT-SIZE: 9pt">@@</span><span lang="EN-US">IDENTITY</span><span style="FONT-FAMILY: 宋体">值。下面的存储过程显示了如何为</span><span lang="EN-US">Northwind</span><span style="FONT-FAMILY: 宋体">示例数据库中的</span><span lang="EN-US">Categories</span><span style="FONT-FAMILY: 宋体">表定义该值。在</span><span lang="EN-US">SQL Query Analyzer</span><span style="FONT-FAMILY: 宋体">中输入这个存储过程，或者运行下载代码中的</span><span lang="EN-US">StoredProcs.sql</span><span style="FONT-FAMILY: 宋体">文件：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="IDENTITY"><span lang="EN-US">CREATE PROCEDURE CategoryInsert(@CategoryName NVARCHAR(15),</span></a></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> @Description NTEXT,</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> @CategoryID INTEGER OUTPUT) AS</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> SET NOCOUNT OFF</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> INSERT INTO Categories (CategoryName, Description)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> VALUES(@CategoryName, @Description)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> SELECT @CategoryID = @@IDENTITY</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">GO</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这将把一个新行插入到</span><span lang="EN-US">Category</span><span style="FONT-FAMILY: 宋体">表中，给调用者返回生成的主键码</span><span lang="EN-US">(CategoryID</span><span style="FONT-FAMILY: 宋体">列的值</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。在</span><span lang="EN-US">Query Analyzer</span><span style="FONT-FAMILY: 宋体">中输入下述</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">命令，可以测试该过程：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">DECLARE @CatID int;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB">EXECUTE CategoryInsert 'Pasties' , 'Heaven Sent Food' , @CatID OUTPUT;</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">PRINT @CatID;</span></p>
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