Question

I’m using Sybase::CTlib to query a Sybase server. However when I execute the following:

while( $dbr->ct_results($restype) == CS_SUCCEED ) {
    if( $restype == CS_CMD_FAIL ) {
    warn "Update Check Failed...";
    next;
    }
    next unless $dbr->ct_fetchable($restype);
    $ts = $dbr->ct_fetch;
}

My query returns exactly one value. Thats why I’m reading into one variable.

I’m getting errors:

Open Client Message:
Message number: LAYER = (1) ORIGIN = (1) SEVERITY = (1) NUMBER = (163)
Message String: ct_results(): user api layer: external error: This routine cannot be called until all fetchable results have been completely processed.

Open Client Message:
Message number: LAYER = (1) ORIGIN = (1) SEVERITY = (1) NUMBER = (159)
Message String: ct_cmd_drop(): user api layer: external error: This routine can be called only if the command structure is idle.

What’s going wrong?

Answer 1

You can not call ct_fetch only once (as your code does), even if your SQL returns one row. You must call it in a loop till false.

brian d foy’s approach seems to be the most consise solution (1 while (my @data = $dbh->ct_fetch); so I won’t bother providing alternatives. What I will provide is the documentation showing why your code failed.

This behavior is documented in SyBooks docs for ct_fetch:

http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.help.sdk_12.5.1.ctref/html/ctref/X65123.htm

If an application does not cancel a result set, it must completely process the result set by calling ct_fetch as long as ct_fetch continues to indicate that rows are available.

The simplest way to do this is in a loop that terminates when ct_fetch fails to return either CS_SUCCEED or CS_ROW_FAIL. After the loop terminates, an application can use a switch-type statement against ct_fetch’s final return code to find out what caused the termination.

If a result set contains zero rows, an application’s first ct_fetch call will return CS_END_DATA.

Note: An application must call ct_fetch in a loop even if a result set contains only a single row. An application must call ct_fetch until it fails to return either CS_SUCCEED or CS_ROW_FAIL.

My un-edicated guess as to the reason is that there’s some "result set completed" flag set internally in CTLib to false and it doesn’t get re-set to true till ct_fetch finds that no more rows are left in the result set (basically, what brian d foy said); and the rest of CTLib code checks that flag and errors out with error 163 when the flag is false.

I can’t confirm that 100% without looking at actual CTLib source code, I wasn’t able to find exact reason in the documentation