81 lines
2.6 KiB
HTML
81 lines
2.6 KiB
HTML
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<html>
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<head>
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<link rel="stylesheet" type="text/css" href="..\styles.css">
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</head>
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<body>
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<img src="..\..\da.png" alt="" align="right">
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<!-------------------------------------------------------------------------->
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<p class="h1">
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<span>Dynamic SQL</span>
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</p>
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<h2>Purpose</h2>
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<p>
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This demo shows how to retrieve schema and/or data via SQL generated at
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runtime.
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</p>
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<p>
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When you compile and run the server, you will see it contains a memo displaying
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"<i>SQL details generated for Update will be displayed here</i>".
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The
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demo does not actually attempt to update server data but merely display
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the fields
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that would be updated by processing the delta. See the <b>TDynSQLService.UpdateData</b>
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code in <b>DynSQLService_Impl</b> to see how the delta is being processed.
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</p>
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<p>
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Having next <b>compiled and run the client</b>, the first thing to try
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is clicking
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on the <b>Retrieve Schema and Data</b> button and you should then see the
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<b>Customers
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data displayed in the grid</b>. Changing the text in the memo, e.g. to
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<b>Select
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* from "Order Details"</b> and clicking the button again results
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in the
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display of a different dataset with a totally different schema. Any of
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the datasets
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in the database (Northwind, by default) may be accessed in this manner.
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</p>
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<p>
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Other points of interest:
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</p>
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<ul>
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<li>
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As their names suggest, the <b>Retrieve Schema</b> and <b>Retrieve Data</b>
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buttons
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achieve the same as the <b>Retrieve Schema and Data</b> button. You might
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want
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to use them separately if the data has the same layout as the schema already
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retrieved.
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For example, having retrieved all the records (<b>Max Records = -1</b>),
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you can
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change the number of records required and select <b>Retrieve Data</b> because
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the schema is correct. If you change the actual SQL though, you will need
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to reload
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the schema.
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</li>
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<li>
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<b>Save</b> and <b>Load</b> buttons. <b>Save</b> stores the schema and
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data in
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<b>Data.dat</b> in the sample folder. If you only want to save the schema,
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set
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Max Records = 0 and retrieve schema and data (otherwise Save cannot work
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because
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the dataset is not open). <b>Load</b> restores the schema and any records
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saved
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no matter what data is currently open. Thus you can think of retrieve and
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load
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as similar operations but with remote and local data respectively.
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</li>
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<li>
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The <b>Update</b> button simulates updating the dataset. You can see the
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result
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in the memo contained in the server form.
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</li>
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</ul>
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</body>
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</html>
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