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From: maury on 14 Apr 2008 06:28
Hello, I have a DB table with data filled from a weather sensor probe,
I have one row every 10 minutes and the data fields is not
in DateTime format but in string format:
yyyyMMddHHmm

So for example I have
200804140340
200804140350
200804140400
200804140410
and so on

I need to write a query in SQL server that "tells" me if there is some
hole
in this table, for example if some data was not retrieved or the
sensor
probe didn't collected for an hour or other time interval...
for example if I have
200804140340
200804140350
200804140410
the query have to spot that the record with 200804140400 date is
missing

Some suggestion about building this query?

Thanks
From: Anith Sen on 14 Apr 2008 10:28
Create table ( temporary table/view/udf or even an SELECT expression that
can be used as a derived table) with yyyyMMddHHmm values starting from the
smallest value to the largest value for that column in your table. Below
you'll see a simple way to create such a table. Now you should be able to
write an simple query using OUTER JOIN or a correlated subquery to get the
list of missing values.

SET NOCOUNT ON
DECLARE @t TABLE( c CHAR(12) NOT NULL PRIMARY KEY) ;
DECLARE @i BIGINT ;
SET @i = 200804140330 ;
WHILE @i < 200804140410 BEGIN
SET @i = @i + 10 ;
IF ( @i % 100 ) < 60
INSERT @t SELECT CAST( @i AS CHAR(12)) ;
END
SELECT * FROM @t ;

To get the missing values, try:

SELECT * FROM @t t
WHERE NOT EXISTS ( SELECT * FROM <your table>
WHERE <your col> = t.c );

--
Anith


From: --CELKO-- on 14 Apr 2008 10:37
Build a look up table of "hhmm" strings (6 periods * 24 hours = 144
rows) then create a query for a given day like this:

SELECT @my_date + T.probe_time
FROM TimeSlots AS T
WHERE @my_date + T.probe_time
NOT IN (SELECT P.probe_time FROM ProbeReadings);

Acutally, an entire year of strings would be only (365 days * 144
slots) = 52560 rows, so you could put this in a VIEW and be ahead of
the game.

From: maury on 15 Apr 2008 12:34
Can I use something similare a FOR statement
in T-SQL?

I wouldn't create a new table with all the rows
(the DB is very 'huge' by now)

Thanks

M.A.

From: --CELKO-- on 15 Apr 2008 13:29
>> Can I use something similar a FOR statement in T-SQL? <<

Technically, yes. It is a WHILE loop. But you are missing the whole
idea of SQL and RDBMS. This is a declarative data retrieval language.
Loops are for procedural, computational languages.

>> I wouldn't create a new table with all the rows (the DB is very 'huge' by now) <<

Huge means Petabytes these days and will soon mean Exabytes. A table
with only 52560 rows is tiny; fill it for ten years and it is still
small-- less than 1 million rows of one column.

If this really bothers you, then set up a table with strings of just
the time slots for a day. Then create a VIEW which uses the
CURRENT_TIMESTAMP, extracts the date from it, concatenates the date
and time together. This VIEW will good for one day at a time. There
might be problems at midnight if the database and the data source are
not in synch.

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