【实施经验】简单理解NC查询引擎中左连接、右连接、内连接、全连接的区别
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">NC的<span style="color: black;">查找</span>引擎中，有左连接（left outer join）、右连接（right outer join）、内连接（inner join）和全连接（full outer join）四种连接方式，区别如下：</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">假设：</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A=1~10，</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">B=5~20，</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">则</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A 左连接 B =1~10</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A 右连接 B =5~20</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A 内连接 B =5~10</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A 全连接 B =1~20</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">常用的<span style="color: black;">通常</span>是左连接。</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">内连接举例：</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">内部交易往来表的客商取值，假设</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A=<span style="color: black;">机构</span>目录</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">B=客商档案</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;"><span style="color: black;">由于</span><span style="color: black;">机构</span>目录中<span style="color: black;">包括</span>了虚拟设置的合并<span style="color: black;">机构</span>，客商档案中又<span style="color: black;">包括</span>了除内部客商以外的客商档案，</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">则：内部交易往来表客商取值=A 内连接 B </span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">全连接举例如下：</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">编制存货收发汇总表，假设：</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">A=存货发出单据数据</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">B=存货入库单据数据</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">C=存货既有入库又有出库的单据数据</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;"><span style="color: black;">由于</span>收发存汇总表<span style="color: black;">必须</span><span style="color: black;">包括</span>存货所有的收入、发出数据，<span style="color: black;">因此呢</span>数据应为<span style="color: black;">A+B+C，</span></span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">则：存货收发汇总表=（<span style="color: black;">A 全连接 B</span>） 全连接 C</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><span style="color: black;">长按<span style="color: black;">照片</span>，识别二维码，关注公众号，谢谢支持！</span></p>
<p style="font-size: 16px; color: black; line-height: 40px; text-align: left; margin-bottom: 15px;"><img src="http://mmbiz.qpic.cn/mmbiz/P0I1fuGabE8asibeslTriaibJ6YxkxBE41bia0H6ibjTFZYxMUKpQFjzSFZfCf6aT4lDYq3allZkzDA02u55ZnR5a7w/640?wx_fmt=jpeg&tp=webp&wxfrom=5&wx_lazy=1&wx_co=1" style="width: 50%; margin-bottom: 20px;"></p>
页:
[1]