RODBC queries returning zero rows

Issue: RODBC (falsely) returning zero rows

Situation:

I'm using RODBC to connect to a DSN I created using a commercial DB's ODBC driver (OSI Soft's PI Historian Time Series DB, if you're curious).

> library(RODBC)
> piconn <- odbcConnect("PIRV", uid = "pidemo")
> sqlStr <- "SELECT tag, time, status, value FROM piinterp WHERE tag = 'PW1.PLANT1.PRODUCTION_RATE' and time > DATE('-4h') and timestep = '+2m'"

Now if I query, I get zero rows.

> sqlQuery(piconn, sqlStr)
[1] TAG    TIME   STATUS VALUE 
<0 rows> (or 0-length row.names)

With BelieveNRows = FALSE these all still show zero results, even though it should return 120 rows.

> sqlQuery(piconn, sqlStr, believeNRows = FALSE)
> sqlQuery(piconn, sqlStr, believeNRows = FALSE, max = 0)
> sqlQuery(piconn, sqlStr, believeNRows = FALSE, max = 0, buffsize = 120)

What else can I try?

Proof that there should be many rows:

In Excel or Command Prompt

SELECT tag, time, status, value FROM piinterp WHERE tag = 'PW1.PLANT1.PRODUCTION_RATE' and time > DATE('-4h') and timestep = '+2m'

With results...

TAG                         TIME            STATUS  VALUE
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:33 448 0
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:31 452 0
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:29 390 0
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:27 419 0
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:25 413 0
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:23 393 0
PW1.PLANT1.PRODUCTION_RATE  15/09/2011 9:21 427 0
etc

Both in R and in Excel, if I query for a tag that doesn't exist, say tag = 'aeeEEEEE11!!!', it correctly returns zero rows.

Additional Info

SQL Tables

> sqlTables(piconn)
   TABLE_QUALIFIER TABLE_OWNER TABLE_NAME TABLE_TYPE  REMARKS
1             <NA>        <NA>    pialias      TABLE  pialias
2             <NA>        <NA>      piavg      TABLE    piavg
3             <NA>        <NA>    pibatch      TABLE  pibatch
4             <NA>        <NA>     picomp      TABLE   picomp
5             <NA>        <NA>   piinterp      TABLE piinterp

ODBC info

> odbcGetInfo(piconn)
       DBMS_Name         DBMS_Ver  Driver_ODBC_Ver Data_Source_Name      Driver_Name       Driver_Ver         ODBC_Ver      Server_Name 
            "PI"     "03.04.0370"          "02.01"           "PIRV"   "PIODBC32.DLL"     "01.03.0100"     "03.52.0000"     "Aurvyzpis1"

My session info :

 sessionInfo()
R version 2.12.2 (2011-02-25)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_Australia.1252  LC_CTYPE=English_Australia.1252    LC_MONETARY=English_Australia.1252 LC_NUMERIC=C                      
[5] LC_TIME=English_Australia.1252    

attached base packages:
[1] grid      stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] ggplot2_0.8.9 proto_0.3-9.2 reshape_0.8.4 plyr_1.6      RODBC_1.3-3  

loaded via a namespace (and not attached):
[1] tools_2.12.2

It turns out that all I needed to do was to set rows_at_time = 1 in addition to believeNRows = FALSE while setting up my ODBC connection.

piconn <- odbcConnect(dsn = "PI", uid = "pwd", believeNRows = FALSE, rows_at_time = 1)
sqlStr <- "SELECT tag, time, status, value FROM piinterp WHERE tag = 'RV1.MADST101_WINDSPEED' and time > DATE('-12h') and timestep = '+2m'"    
results <- sqlQuery(piconn, sqlStr)

Try adding

believeNRows = FALSE

to the query. This is an issue that has come up with a few of the drivers which report a wrong size on the result set.

Test if the ODBC driver works correctly. Each ODBC driver should provide simple means to test the connection. Also try to connect to the ODBC source using MS Office (Access, Excel...) or Open Office.
If the above works, then go to R and try the simplest query possible, like select 1 (your query isn't the simplest, as darcken noted! You have to try really the simplest query to be sure).
If it doesn't work, try to call odbcGetErrMsg() function after each RODBC function call (after connect, after query, ...).

I had the same problem and fixed it by adding "rows_at_time=1" to the odbcConnect call. From the odbcConnect help:

*Several errors which have been reported as bugs in RODBC 1.3-0 which were in fact ODBC driver errors that can be circumvented by setting rows_at_time = 1 (and the warning under that argument has always been there). The drivers involved have been third-party Oracle drivers and old SQL Server drivers.*

In my case I was running 64bit R 2.15.0, RODBC 1.3-5 and the Actual ODBC Oracle driver on OS X Lion.

I think you need to rule out that your actually connecting to the database/table first by getting SELECT * FROM MYTABLE to work within R. If you can't get this working then something is wrong with your setup/drivers.

Once you are sure that you can actually query the database/table within R then progressively make your query more complex and try to isolate where the issue is. One thing to try might be double == on your equality conditions.

I've tried using a bunch of databases(sql server,mysql,sqlite) within R and the performance has been poor with all of them. Imo your better off querying the database natively, dumping to text, then reading the file into R.

来源：https://stackoverflow.com/questions/7425100/rodbc-queries-returning-zero-rows

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