如何通过DATE值常量过滤FireDAC数据集？ [英] How to filter FireDAC dataset by a DATE value constant?

问题描述

procedure TForm2.Button1Click(Sender: TObject);
begin
  with qryWithFilter do
  begin
    Filtered := False;
    OnFilterRecord := nil;
    // date separator may be used any from [' ', '-', '\', '.', '/']
    // Filter := 'DATA_NAS < (''DatetoStr(date3)'')';
    // Filter := 'DATA_NAS < ''28/06/1939''';
    // Filter := 'DATA_NAS < (FormatDateTime(''dd/mm/yyyy'', ''28/06/1968''))';
    // Filter := 'DATA_NAS < TO_DATE(''1996-07-29'',''yyyy-mm-dd'')';
    Filter := 'DATA_NAS < (TO_DATE(''1996-07-29'',''yyyy-mm-dd''))';
    Filtered := True;
  end;
end;

仅与 ’28 / 06/1968一起使用。我得到的错误是：

Only work with ''28/06/1968''. The error I'm getting is:

如何通过DATE值常量过滤FireDAC查询？

How can I filter my FireDAC query by a DATE value constant?

推荐答案

FireDAC的 过滤器 属性实现不支持DBMS功能，但为您提供了自己的表达式引擎。

The FireDAC's Filter property implementation doesn't support DBMS functions, but offers you their own expression engine.

使用FireDAC将字符串常量转换为 日期 在 过滤器 属性表达式可以像使用 转换 宏功能或 {d} 转义序列。然后，表达式引擎为您选择特定于DBMS的转换函数。

With FireDAC converting a string constant into a DATE type value in the Filter property expression can be as simple as using the CONVERT macro function or {d} escape sequence. The expression engine then picks a DBMS specific conversion function for you.

尝试以下过滤器之一（所有变体的日期字符串格式为 yyyy-mm-dd ）：

Try one of these filters (date string format for all variants is yyyy-mm-dd):

uses
  FireDAC.Stan.ExprFuncs;

procedure TForm1.Button1Click(Sender: TObject);
begin
  with FDQuery do
  begin
    { disable filter }
    Filtered := False;
    { filter with date escape sequence (is nicely readable) }
    Filter := 'DATA_NAS < {d 1996-07-29}';
    { filter with CONVERT macro function without function escape sequence }
    Filter := 'DATA_NAS < {CONVERT(''1996-07-29'', DATE)}';
    { filter with CONVERT macro function with function escape sequence }
    Filter := 'DATA_NAS < {fn CONVERT(''1996-07-29'', DATE)}';
    { enable filter }
    Filtered := True;
  end;
end;

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