Re: Is it possible to call find the number of columns in a JDBC query without executing it?

From: Robert Klemme (bob.news_at_gmx.net)
Date: 02/23/04

  • Next message: Rob: "searching for a nice database" 
    Date: Mon, 23 Feb 2004 18:07:08 +0100

    Sorry for jumping in lately. I might repeat things that have been said
    before.

    "Jeff Smith" <jsmit234 at ford dot com> schrieb im Newsbeitrag
    news:c1cv6r$47h6@eccws12.dearborn.ford.com...
    > That is a good solution (David Harper's forcing query to execute but
    return
    > nothing). You may also be able to actually query the database system
    tables
    > for column and/or counts. In Oracle's case, all_tab_columns. Other
    dbms's
    > should have similar tables, but you definitely lose portability this
    way.
    >
    > This still involves an actual *query* of some kind being round-tripped,
    > albeit very quick.

    That's what DatabaseMetaData is for:
    http://java.sun.com/j2se/1.4.2/docs/api/java/sql/Connection.html#getMetaData()
    http://java.sun.com/j2se/1.4.2/docs/api/java/sql/DatabaseMetaData.html

    The downside is that is easy only for queries like "select * from foo"
    i.e. when you simply draw data from a table, but it doesn't work well for
    real queries which might involve conversions of column types, joins etc.

    > Jeff
    >
    > "David Harper" <devnull@obliquity.u-net.com> wrote in message
    > news:Jw6Zb.54$m47.9@newsfe1-win...
    > > Geoff Hardy wrote:
    > >
    > > > Is it possible to call find the number of columns in a query without
    > > > executing it?
    > > [SNIP]
    > >
    > > You could try appending "LIMIT 1" to your query, then you *can*
    execute
    > > it, safe in the knowledge that you aren't about to suck a couple of
    > > gigabytes of data out of Oracle just to count the columns.

    When talking about portability, wouldn't it be better to add something
    like "1 = 0" (i.e. always false) to the WHERE clause? IMHO this is more
    portable than using LIMIT or TOP (MS SQL Server) and ensures that the
    result set is empty, too.

    > > The metadata for the limited query will be the same as for the full
    query.

    Yes.

        robert

  • Next message: Rob: "searching for a nice database"

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