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21.3 命令
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21.3 命令
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165596.htm'>21.2 使用数据库连接</a></div><div style='float:right;width:49%'>·<a href='100165597.htm'>21.2.1 高效地使用连接</a></div><div style='float:left;width:49%'>·<a href='100165598.htm'>21.2.2 事务处理</a></div><div style='float:right;width:49%'>·<a href='100165600.htm'>21.3.1 执行命令</a></div><div style='float:left;width:49%'>·<a href='100165601.htm'>21.3.2 调用存储过程</a></div><div style='float:right;width:49%'>·<a href='100165602.htm'>21.4 快速数据访问：数据读取器</a></div></div>
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<link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 11.4pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 11.4pt"><a ftel="_Toc507815160"><span lang="EN-GB">21.3 </span></a><span style="FONT-FAMILY: 楷体_GB2312">命令</span></h3>
<p class="MsoNormal"><a ftel="commands"><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">21.2</span></a><span style="FONT-FAMILY: 宋体">节中简要介绍了针对数据库执行的命令。简言之，命令就是一个要在数据库上执行的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">文本字符串。命令也可以是一个存储过程，或者返回表中所有列和所有行的表名</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">例如</span><span lang="EN-US">SELECT *</span><span style="FONT-FAMILY: 宋体">样式的子句</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">把</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">子句作为一个参数传递给</span><span lang="EN-US">Command</span><span style="FONT-FAMILY: 宋体">类的构造函数，就可以构造一个命令，如下</span><span lang="EN-US"> </span><span style="FONT-FAMILY: 宋体">所示：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">string source = "server=(local)\\NetSDK;" +</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB"> "</span><span lang="EN-GB"> </span><span lang="EN-GB">integrated security=SSPI;" + </span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB"> "database=Northwind";</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB">string select = "SELECT ContactName,CompanyName FROM Customers";</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB">SqlConnection conn = new SqlConnection(source);</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB">conn.Open();</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-GB"> </span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">SqlCommand cmd = new SqlCommand(select, conn);</span></p>
<p class="MsoNormal"><span lang="EN-GB"><provider></span><span lang="EN-US">Command</span><span style="FONT-FAMILY: 宋体">类的属性</span><span lang="EN-US">CommandType</span><span style="FONT-FAMILY: 宋体">可以定义某个命令是一个</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">子句、一个存储过程的调用</span><span style="FONT-FAMILY: 宋体">、或者</span><span style="FONT-FAMILY: 宋体">是一个完整的表语句</span><span lang="EN-GB">(</span><span style="FONT-FAMILY: 宋体">仅从给定的表中选择所有的列和行</span><span lang="EN-GB">)</span><span style="FONT-FAMILY: 宋体">。表</span><span lang="EN-US">21-2</span><span style="FONT-FAMILY: 宋体">总结了</span><span lang="EN-US">CommandType</span><span style="FONT-FAMILY: 宋体">枚举</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="a5" style="MARGIN-TOP: 8.15pt"><span style="FONT-FAMILY: 黑体">表</span><span lang="EN-US"> 21-2</span></p>
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<td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 9.9pt; BORDER-TOP: windowtext 1pt solid; PADDING-LEFT: 9.9pt; BORDER-LEFT-WIDTH: 1pt; BORDER-LEFT-COLOR: windowtext; PADDING-BOTTOM: 0cm; WIDTH: 105.5pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid" valign="top" width="141">
<p class="a2"><a ftel="CommandType"><span style="FONT-FAMILY: 黑体">命</span> </a><span style="FONT-FAMILY: 黑体">令</span> <span style="FONT-FAMILY: 黑体">类</span> <span style="FONT-FAMILY: 黑体">型</span></p>
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<p class="a2"><span style="FONT-FAMILY: 黑体">样</span><span lang="EN-US"> </span><span style="FONT-FAMILY: 黑体">例</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">Text(</span><span style="FONT-FAMILY: 宋体">默认</span><span lang="EN-US">)</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">String select = "SELECT ContactName FROM Customers";</span></p>
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">SqlCommand cmd = new SqlCommand</span><span lang="EN-GB">(</span><span lang="EN-US">select</span><span style="FONT-FAMILY: 宋体">，</span><span lang="EN-US">conn</span><span lang="EN-GB">);</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">StoredProcedure</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">SqlCommandcmd=new SqlCommand("CustOrderHist"</span><span style="FONT-FAMILY: 宋体">，</span><span lang="EN-US">conn); </span></p>
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">cmd.CommandType = CommandType.StoredProcedure</span><span lang="EN-GB">;</span></p>
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">cmd.Parameters.Add</span><span lang="EN-GB">(</span><span lang="EN-US">"@CustomerID"</span><span style="FONT-FAMILY: 宋体">，</span><span lang="EN-US">"QUICK"</span><span lang="EN-GB">);</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">TableDirect</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">OleDbCommand cmd = new OleDbCommand</span><span lang="EN-GB">(</span><span lang="EN-US">"Categories"</span><span style="FONT-FAMILY: 宋体">，</span><span lang="EN-US">conn</span><span lang="EN-GB">);</span></p>
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">cmd.CommandType = CommandType.TableDirect;</span></p>
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<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在执行一个存储过程时，需要把参数传送给过程。上面的示例直接设置了参数</span><span lang="EN-US">@CustomerID</span><span style="FONT-FAMILY: 宋体">，但设置参数的值还可以使用其他方式，详见本章的后面。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; FTEL: 21.45pt"><span style="FONT-FAMILY: 黑体">提示：</span></p>
<p class="a1" style="FTEL: 21.45pt"><span lang="EN-US">TableDirect</span><span style="FONT-FAMILY: 楷体_GB2312">命令类型只对</span><span lang="EN-US">OleDb</span><span style="FONT-FAMILY: 楷体_GB2312">提供程序有效</span><span style="FONT-FAMILY: 黑体; LETTER-SPACING: -1pt">——</span><span style="LETTER-SPACING: -1pt"> </span><span style="FONT-FAMILY: 楷体_GB2312">如果试图把这个命令类型用于其他提供程序，就会产生异常。</span></p></div>
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