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Re^4: fetchall_arrayref hangs with placeholders query with no results

by afoken (Chancellor)
on Apr 29, 2021 at 10:39 UTC ( #11131860=note: print w/replies, xml ) Need Help??

in reply to Re^3: fetchall_arrayref hangs with placeholders query with no results
in thread fetchall_arrayref hangs with placeholders query with no results

The untyped variable ? is allowed only in ...

That's a problem of missing type information and does not make select ? completely illegal in all SQL implementations, not even in Sybase ASE.

Try adding type information like I did for PostgreSQL. Actually, just copy my PostgreSQL example and change the connect line to connect to Sybase. I would expect that to work in Sybase ASE.

Should that fail, try to cast the (untyped) placeholder to a type. According to my first google result, SELECT CAST(? AS NUMERIC) ANSWER should do the trick.


Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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Re^5: fetchall_arrayref hangs with placeholders query with no results
by mpeppler (Vicar) on Apr 29, 2021 at 12:12 UTC
    No - that syntax is indeed illegal in Sybase ASE (and I suspect MS-SQL).

    This has nothing to do with the placeholder type - it's because the main point of placeholders is performance - it's so that you can re-use a SQL statement many times with different parameters without having to re-compile and re-optimize it. With a complex SQL query this can make a very big difference in performance (SQL parsing and optimization can take many 100s of milliseconds, much more that the actual fetching of the data on a large system).

    With Sybase and MS-SQL what happens is that DBD::Sybase detects that one or more ?-style placeholders are in the SQL statement. This is then passed to the ct_dynamic() API, which performs the "prepare" step on the server, identifies the parameter types (based on the column types in the WHERE clause) and returns a handle to this prepared statement. This is now basically a temporary stored procedure.

    DBD::Sybase has never done any client-side placeholder processing.

    Personally I fail to see the point of using placeholders in the SELECT clause, unless there's some weird variable quoting issue that the OP wants to handle.

    BTW - the DBI docs also state that ?-style placeholders will normally only work in WHERE or VALUES clauses:


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