20 lines
2.5 KiB
HTML
20 lines
2.5 KiB
HTML
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<p>sql server支持变量所以一般使用方法如下：</p>
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<div class="cnblogs_code">
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<pre><span style="color: #0000ff;">DECLARE</span> <span style="color: #008000;">@Val</span> <span style="color: #0000ff;">varchar</span>(<span style="color: #800000; font-weight: bold;">50</span><span style="color: #000000;">)
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</span><span style="color: #0000ff;">select</span> <span style="color: #008000;">@Val</span> <span style="color: #808080;">=</span> param_value <span style="color: #0000ff;">where</span> t_param <span style="color: #0000ff;">where</span> param_name <span style="color: #808080;">=</span> <span style="color: #ff0000;">'</span><span style="color: #ff0000;">log_type</span><span style="color: #ff0000;">'</span>
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<span style="color: #0000ff;">if</span>(<span style="color: #008000;">@Val</span> <span style="color: #0000ff;">is</span> <span style="color: #0000ff;">null</span><span style="color: #000000;">)
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</span><span style="color: #0000ff;">begin</span>
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<span style="color: #0000ff;">select</span> <span style="color: #008000;">@Val</span> <span style="color: #808080;">=</span> param_default_value <span style="color: #0000ff;">where</span> t_param_info <span style="color: #0000ff;">where</span> param_name <span style="color: #808080;">=</span> <span style="color: #ff0000;">'</span><span style="color: #ff0000;">log_type</span><span style="color: #ff0000;">'</span>
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<span style="color: #0000ff;">end</span>
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<span style="color: #0000ff;">select</span> <span style="color: #008000;">@Val</span></pre>
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</div>
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<p> </p>
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<p>mysql中执行语句时不支持定义变量及条件判断，所以想了个办法，也能达到相同目的</p>
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<p> </p>
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<div class="cnblogs_code">
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<pre><span style="color: #0000ff;">SELECT</span><span style="color: #000000;"> IFNULL(
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(</span><span style="color: #0000ff;">select</span> param_value <span style="color: #0000ff;">from</span> t_param <span style="color: #0000ff;">where</span> param_name <span style="color: #808080;">=</span> <span style="color: #ff0000;">'</span><span style="color: #ff0000;">log_type</span><span style="color: #ff0000;">'</span><span style="color: #000000;">),
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(</span><span style="color: #0000ff;">select</span> param_default_value <span style="color: #0000ff;">from</span> t_param_info <span style="color: #0000ff;">where</span> param_name <span style="color: #808080;">=</span> <span style="color: #ff0000;">'</span><span style="color: #ff0000;">log_type</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)
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) </span><span style="color: #0000ff;">as</span> param_value;</pre>
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</div>
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<p> </p>
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