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Posted by Shelly on 09/17/07 17:25
"jbl" <jbl@profisystem.info> wrote in message
news:1190049012.382175.69020@n39g2000hsh.googlegroups.com...
> Hello.
> I would like to select only changes in value:
> time (datetime)
> bits (integer)
> in command:
> select time,(bits>>8)&1 as P from VV order by time
> I view this result:
> time P
> 12:23:11 0
> 12:23:16 0
> 12:24:01 0
> 12:24:10 1
> 12:24:23 1
> 12:24:45 0
> 12:25:01 0
> 12:25:34 1
> 12:25:59 1
>
> And how to obtain this result:
> 12:23:11 0
> 12:24:10 1
> 12:24:45 0
> 12:25:34 1
>
> The group clause selects only two rows:
> 12:23:11 0 the first "0" value
> 12:24:10 1 the first "1" value
>
> Can you help me?
>
I don't know how you could do this automatically with sql, but you could
foreach your way through the set, remembering the last P value and, if it
changes, then ooutput that row and reset the the remembered P value. Here
is some pseudocode.
P0 = 2;
foreach loop {
read next row from returned mysql query resource
get P and time from this row
if (P != P0) {
P0 = P;
output time and P
}
}
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