sql - Percentage difference between numbers in two columns -

my sql experience minimal please go easy on me here. have table tblforex , i'm trying create query looks @ 1 particular column lastsalesratechangedate , forexrate.

basically want query check lastsalesratechangedate , pull forexrate on same line (obviously in forexrate column), need check see if there +/- 5% change since last time lastsalesratechangedate changed. hope makes sense, tried explain possible.

i believe need create 'subquery' @ lastsalesratechangedate , pull forex rate date, don't know how go this.

i should add being done in access (sql)

sample data, here table looks like:

| basecur | forcur | forexrate | lastsalesratechangedate | usd     | brl    | 1.718     | 12/9/2008       | usd     | brl    | 1.65      | 11/8/2008 

so need query @ lastsalesratechangedate column, check see if date has changed, if take forexrate value , give percentage difference of forexrate value since last record.

so final result like

"basecur" "forcur" "percentage change since last sales rate change" usd         brl            x% 

gordon's answer pointed in right direction:

select t2.*, (select top 1 t.forexrate tblforex t t.basecur=t2.basecur , t.forcur=t2.forcur , t.lastsalesratechangedate<t2.lastsalesratechangedate order t.lastsalesratechangedate desc, t.forexrate desc ) previousrate, [forexrate]/[previousrate]-1 changeratio tblforex t2; 

access gives errors top 1 in subquery causes "ties". broke ties , therefore removed error adding item order by clause. ratio display percentage, switch design view , change properties of column accordingly.