数据库入门

  • 左连接
    特点:返回包括左表中所有记录和右表中连接字段相等的记录。
    -右连接
    特点:返回右表中所有记录和左表中连接字段相等的记录
    在这里插入图片描述
  • 内连接
    特点:只有满足条件的记录才能出现在结果关系中
    在这里插入图片描述
PI数据库开发SDK例程 The introduction provides an architectural overview of how the PI-SDK fits into various programming environments. A description and simplified view of the PI-SDK object model is also presented. What Is the PI-SDK? The PI Software Development Kit (PI-SDK) is a programming tool providing access to PI Servers. The software consists of an ActiveX in-process server, an ActiveX control, and supporting code libraries. The kit comes with online documentation, example code, various support files, and tools. The PI-SDK runs on 32-bit Windows platforms and provides access to servers on all PI platforms. Based on Microsoft’s Component Object Model (COM), the PI-SDK can be used with most WIN32 programming environments. The kit is particularly well integrated with Microsoft Visual Basic providing rapid development and deployment of PI applications. The PI-SDK provides an object-oriented approach to program interaction with PI Systems. It delivers a hierarchical model of objects and collections representing the components of PI Servers. This approach provides for intuitive and efficient access. What Documentation Is Provided? The PI-SDK User Guide and the PI-SDK Programming Reference are the primary sources for information related to the PI-SDK. Both are incorporated in the online help system. A version of the user guide in MS Word format is also installed during the setup for printing or for use in training programs. Programming Reference Detailed programming references for properties and methods of each object in the PI-SDK and the PI-SDK Control and Dialogs are available in online help. Most methods provide an example of their usage in Visual Basic. Other code examples, including examples of calling the PI-SDK
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