用mapbasic中 fetch怎么用，求解释每一句，特别是fetch first from asdf，运行时显示找不到asdf文件。。
include"mapbasic.def"declaresubmaindeclaresubdrawpointsubmaincalldrawpointendsubsubdr...
include "mapbasic.def"
declare sub main
declare sub drawpoint
sub main
call drawpoint
end sub
sub drawpoint
dim x as float
dim y as float
dim i as integer
i = 1
fetch first from asdf
do until eot(asdf)
x = asdf.a
y = asdf.b
note x
update asdf set obj = CreatePoint(x, y) where rowid = i
i = i + 1
fetch next from asdf
loop
end sub 展开
declare sub main
declare sub drawpoint
sub main
call drawpoint
end sub
sub drawpoint
dim x as float
dim y as float
dim i as integer
i = 1
fetch first from asdf
do until eot(asdf)
x = asdf.a
y = asdf.b
note x
update asdf set obj = CreatePoint(x, y) where rowid = i
i = i + 1
fetch next from asdf
loop
end sub 展开
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