042.htm

Delphi基础知识讲座

<p>end;</p>
<p>end;</p>
<p>　</p>
<p>procedure TQueryForm.BitBtn2Click(Sender: TObject);</p>
<p>var</p>
<p>strAlias, { Alias name selected by the user }</p>
<p>strTable, { Table name selected by the user }</p>
<p>strField, { Field name selected by the user }</p>
<p>strValue, { Field Value entered by the user }</p>
<p>strWhere, { WHERE clause for the user's query }</p>
<p>strQuote, { Holds quotes is the query field is text }</p>
<p>strQuery: string; { String used to construct the query }</p>
<p>frmQuery: TResultForm; { The Results form }</p>
<p>type</p>
<p>　</p>
<p>{ The following type is used with the Type drop-down</p>
<p>list. The text values corresponding with each item is</p>
<p>described in comments, along with the relevant SQL operators. }</p>
<p>　</p>
<p>etSQLOps = (soNoCondition, { not field conditions: no WHERE clause }</p>
<p>soEqual, { equals: = }</p>
<p>soNotEqual, { is not equal to: &lt;&gt; }</p>
<p>soLessThan, { is less than: &lt; }</p>
<p>soLessEqual, { is less than or equal to: &lt;= }</p>
<p>soMoreThan, { is greater than: &gt; }</p>
<p>soMoreEqual, { is greater than or equal to: &gt;= }</p>
<p>soStartsWith, { starts with: LIKE xx% }</p>
<p>soNoStartsWith, { doesn't start with: NOT LIKE xx% }</p>
<p>soEndsWith, { ends with: LIKE %xx }</p>
<p>soNoEndsWith, { doesn't end with: NOT LIKE %xx }</p>
<p>soContains, { contains: LIKE %xx% }</p>
<p>soNoContains, { doesn't contain: NOT LIKE %xx% }</p>
<p>soBlank, { is blank: }</p>
<p>soNotBlank, { is not blank: }</p>
<p>soInside, { contains only: IN ( xx, yy, zz ) }</p>
<p>soOutside); { doesn't contain: NOT IN (xx, yy, zz) }</p>
<p>begin</p>
<p>　</p>
<p>{ Initialize the variables needed to run the query }</p>
<p>　</p>
<p>with ListBox1 do</p>
<p>if ItemIndex = -1 then</p>
<p>raise Exception.Create('Can''t Run Query: No Alias Selected')</p>
<p>else</p>
<p>strAlias := Items.Strings[ItemIndex];</p>
<p>　</p>
<p>with ListBox2 do</p>
<p>if ItemIndex = -1 then</p>
<p>raise Exception.Create('Can''t Run Query: No Table Selected')</p>
<p>else</p>
<p>strTable := Items.Strings[ItemIndex];</p>
<p>　</p>
<p>with ListBox3 do</p>
<p>if ItemIndex = -1 then</p>
<p>begin</p>
<p>if ComboBox1.ItemIndex &gt; Ord(soNocondition) then</p>
<p>raise Exception.Create('Can''t Run Query: No Field Selected')</p>
<p>else</p>
<p>strField := '';</p>
<p>end</p>
<p>else</p>
<p>strField := Items.Strings[ItemIndex];</p>
<p>　</p>
<p>if (Edit1.Text = '') and</p>
<p>(ComboBox1.ItemIndex &gt; Ord(soNoCondition)) and</p>
<p>(ComboBox1.ItemIndex &lt; Ord(soBlank)) then</p>
<p>raise Exception.create('Can''t Run Query: No Search Value Entered')</p>
<p>else</p>
<p>strValue := Edit1.Text;</p>
<p>　</p>
<p>{ See if the field being search is a string field. If so, then pad the</p>
<p>quote string with quotation marks; otherwise, set it to a null value. }</p>
<p>　</p>
<p>if strField &lt;&gt; '' then</p>
<p>with Table1.FieldByName(strField) do</p>
<p>if (DataType = ftString) or (DataType = ftMemo) then</p>
<p>strQuote := '&quot;' else</p>
<p>strQuote := '';</p>
<p>　</p>
<p>{ Construct the WHERE clause of the query based on the user's choice</p>
<p>in Type. }</p>
<p>　</p>
<p>case etSQLOps(ComboBox1.ItemIndex) of</p>
<p>soNoCondition: strWhere := '';</p>
<p>soEqual: strWhere := strField + ' = ' + strQuote + strValue+ strQuote;</p>
<p>soNotEqual: strWhere := strField + ' &lt;&gt; ' + strQuote + strValue +</p>
<p>strQuote;</p>
<p>soLessThan: strWhere := strField + ' &lt; ' + strQuote + strValue +</p>
<p>strQuote;</p>
<p>soLessEqual: strWhere := strField + ' &lt;= ' + strQuote + strValue +</p>
<p>strQuote;</p>
<p>soMoreThan: strWhere := strField + ' &gt; ' + strQuote + strValue +</p>
<p>strQuote;</p>
<p>soMoreEqual: strWhere := strField + ' &gt;= ' + strQuote + strValue +</p>
<p>strQuote;</p>
<p>soStartsWith: strWhere := strField + ' LIKE ' + strQuote +</p>
<p>strValue + '%' + strQuote;</p>
<p>soNoStartsWith: strWhere := strField + ' NOT LIKE ' + strQuote +</p>
<p>strValue + '%' + strQuote;</p>
<p>soEndsWith: strWhere := strField + ' LIKE ' + strQuote +</p>
<p>'%' + strValue + strQuote;</p>
<p>soNoEndsWith: strWhere := strField + ' NOT LIKE ' +</p>
<p>strQuote + '%' + strValue + strQuote;</p>
<p>soContains: strWhere := strField + ' LIKE '+ strQuote+'%'+ strValue</p>
<p>+ '%' + strQuote;</p>
<p>soNoContains: strWhere := strField + ' NOT LIKE ' + strQuote + '%'</p>
<p>+ strValue + '%' + strQuote;</p>
<p>soBlank: strWhere := strField + ' IS NULL';</p>
<p>soNotBlank: strWhere := strField + ' IS NOT NULL';</p>
<p>end;</p>
<p>　</p>
<p>if ComboBox1.ItemIndex = Ord(soNoCondition) then</p>
<p>strQuery := 'SELECT * FROM &quot;' + strTable + '&quot;'</p>
<p>else if Table1.FieldByName(strField).DataType = ftString then</p>
<p>strQuery := 'SELECT * FROM &quot;' + strTable + '&quot; t WHERE t.' + strWhere</p>
<p>else</p>
<p>strQuery := 'SELECT * FROM &quot;' + strTable + '&quot; t WHERE t.' + strWhere;</p>
<p>　</p>
<p>{ Create an instance of the browser form. }</p>
<p>frmQuery := TResultForm.Create(Application);</p>
<p>　</p>
<p>{ Use a resource protection block in case an exception is raised. This</p>
<p>ensures that the memory allocated for the Results form is released. }</p>
<p>try</p>
<p>with frmQuery do</p>
<p>begin</p>
<p>Screen.Cursor := crHourglass;</p>
<p>if Query1.Active then Query1.Close;</p>
<p>Query1.DatabaseName := strAlias; {set the alias the query poitns to}</p>
<p>Query1.SQL.clear; { empty existing SQL in the query }</p>
<p>Query1.SQL.Add(strQuery); { add query string to query object }</p>
<p>Query1.Active := True; { try to run the query }</p>
<p>Screen.Cursor := crDefault;</p>
<p>　</p>
<p>if Query1.Active then</p>
<p>begin</p>
<p>{ If the query didn't return any records, there's no point in</p>
<p>displaying the form. In that event, raise an exception. }</p>
<p>if Query1.RecordCount &lt; 1 then</p>
<p>raise Exception.create('No records matched your criteria. </p>
<p>Please try again.' );</p>
<p>　</p>
<p>{ write a message to the browse form's status line }</p>
<p>if strField = '' then</p>
<p>Panel3.Caption := 'Now showing all records from ' + strTable </p>
<p>+ '...'</p>
<p>else</p>
<p>Panel3.Caption := 'Now showing '+ strTable +' where '+ strField</p>
<p>+' contains values equal to '+ strValue + '...';</p>
<p>　</p>
<p>{ show the form }</p>
<p>ShowModal;</p>
<p>end;</p>
<p>end;</p>
<p>finally</p>
<p>frmQuery.Free;</p>
<p>end;</p>
<p>end;</p>
<p>　</p>
<p>end.</p>
<p>　</p>
<p>　</p>
<p>unit RSLTFORM;</p>
<p>　</p>
<p>interface</p>
<p>　</p>
<p>uses</p>
<p>SysUtils, Windows, Messages, Classes, Graphics, Controls, StdCtrls, DB,</p>
<p>Forms, DBCtrls, DBGrids, DBTables, Buttons, Grids, ExtCtrls, Dialogs;</p>
<p>　</p>
<p>type</p>
<p>TResultForm = class(TForm)</p>
<p>DBGrid1: TDBGrid;</p>
<p>DBNavigator: TDBNavigator;</p>
<p>Panel1: TPanel;</p>
<p>DataSource1: TDataSource;</p>
<p>Panel2: TPanel;</p>
<p>Panel3: TPanel;</p>
<p>Query1: TQuery;</p>
<p>SpeedButton2: TSpeedButton;</p>
<p>Panel4: TPanel;</p>
<p>SpeedButton1: TSpeedButton;</p>
<p>procedure SpeedButton1Click(Sender: TObject);</p>
<p>procedure SpeedButton2Click(Sender: TObject);</p>
<p>end;</p>
<p>　</p>
<p>var</p>
<p>ResultForm: TResultForm;</p>
<p>　</p>
<p>implementation</p>
<p>　</p>
<p>{$R *.DFM}</p>
<p>　</p>
<p>procedure TResultForm.SpeedButton1Click(Sender: TObject);</p>
<p>begin</p>
<p>Close;</p>
<p>end;</p>
<p>　</p>
<p>procedure TResultForm.SpeedButton2Click(Sender: TObject);</p>
<p>var</p>
<p>strText: string; { Variable to hold display text }</p>
<p>iCounter: Integer; { Loop counter variable }</p>
<p>begin</p>
<p>　</p>
<p>{ Build a string containing the query }</p>
<p>　</p>
<p>strText := '';</p>
<p>for iCounter := 0 to Query1.SQL.Count - 1 do</p>
<p>strText := strText + Query1.SQL[iCounter];</p>
<p>　</p>
<p>{ Display the query text }</p>
<p>　</p>
<p>MessageDlg('The underlying query is: ' + #10 + #10 + strText,</p>
<p>mtInformation, [mbOK], 0 );</p>
<p>end;</p>
<p>　</p>
<p>end.</p>
<p>　</p>
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