怎么实现排序功能

如何实现排序功能
表单中,有一个表.

表中,有一个字段"日期". (datetime型)

要求是:

当单击此字段名,则升序排列

再次点击,则降序排列.

不知如何写代码,我用的是VFP 9.0 +SQL

[解决办法]
在这个表格日期列的标头 thisform.grid1.column1.header1.click 事件过程中,更改表格的recordsource 定义,改变其 sql 语句中的 order by 子句的排序方向.
[解决办法]

C/C++ code

*OrderBy 自定义属性，为 .F. 表示 asc， .T. 表示 desc，初始化为.F.*HeaderCaption 自定义属性，用来保存上一次排序使用的列名，出事化为空（“”），字符型LOCAl array laEvEnts[1]Aevents(laEvEnts,0)obj_name = laEvEnts[1,1]lcHeaderName = obj_name.captionIf At('▲',lcHeaderName) != 0 Or At('▼',lcHeaderName) != 0    lcHeaderName = Substr(lcHeaderName, 1, Len(lcHeaderName) - 2) && 如果列名带有▼或▲ ，则先去除Endif If Alltrim(lcHeaderName) != Alltrim(thisform.HeaderCaption)    thisform.OrderBy = .F.    thisform.HeaderCaption = lcHeaderName    For i = 2 To 19        lcColumn = 'Column' + Transform(i)        lcTempString = thisform.container1.grid1.&lcColumn..header1.caption        If At('▲',lcTempString) != 0 Or At('▼',lcTempString) != 0 && 当不是鼠标点击的列的时候，去除列标题中的 ▼或▲            thisform.container1.grid1.&lcColumn..header1.caption = Substr(lcTempString,1,Len(lcTempString) - 2)            Exit        Endif     Next     obj_name.caption = obj_name.caption + '▼'Else    thisform.HeaderCaption = Substr(lcHeaderName,1,Len(lcHeaderName) - 2)    If thisform.OrderBy = .F.        thisform.OrderBy = .T.        obj_name.caption = lcHeaderName + '▲'    Else        thisform.OrderBy = .F.        obj_name.caption = lcHeaderName + '▼'    Endif Endif thisform.container1.grid1.RecordSource = NULLIf Thisform.OrderBy = .F. && 已经从sql数据库中查询成成了 temp 临时表，用temp 作为查询源    Select * From temp Order By &lcHeaderName. Into Cursor tmp    Select * From tmp Into Cursor tempElse    Select * From temp Order By &lcHeaderName. Desc Into Cursor tmp    Select * From tmp Into Cursor tempEndif thisform.container1.grid1.RecordSource = 'temp'thisform.container1.grid1.AutoFit thisform.container1.grid1.column1.Width = 0Go (thisform.lnLine)thisform.container1.grid1.SetFocus thisform.container1.grid1.Refresh