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Newsgroups: comp.lang.java.databases
Date: Mon, 15 Feb 2016 09:15:28 -0800 (PST)
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Subject: Re: Getting the size of a result set
From: jagilberte@gmail.com
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Xref: csiph.com comp.lang.java.databases:725

El jueves, 8 de marzo de 2001, 18:02:04 (UTC+1), Valentin Todorov  escribi=
=F3:
> Try this:
>=20
>     long getCount(Connection con, String table){
>         Statement stmt =3D null;
>         ResultSet rs =3D null;
>         int count =3D 0;
>         try{
>             stmt =3D con.createStatement();
>             rs =3D stmt.executeQuery("SELECT COUNT(*) FROM "+table);
>             if(rs.next())
>                 count =3D rs.getInt(1);
>         }catch(SQLException e) {
>             // error handling
>         }finally{
>             // close rs &stmt
>         }
>     }
>=20
> HTH
> Valentin
>=20
>=20
> Jon Skeet schrieb:
>=20
> > Hi everyone,
> >
> > I'm not new to Java, but I'm extremely new to JDBC, SQL, and the whole
> > database "thang". I've been tasked with writing a class to implement ou=
r
> > own data interface, but accessing a JDBC database. One of the methods I
> > have to implement is (on a ResultSet-type object) getCount() which
> > should return the number of rows in the results.
> >
> > I've been trying to figure out a way of doing this using JDBC, and I
> > haven't got very far yet. As this is only a prototype at the moment, I'=
m
> > probably okay to use any standard JDBC extensions etc if necessary,
> > although obviously I'd like to keep it as simple as possible. I'd hoped
> > that ResultSetMetaData would have something in it, or that I could
> > specify an OUT parameter in a PreparedStatement which could contain the
> > count. (I realise I can use OUT parameters with a CallableStatement, bu=
t
> > I can't force our users to add appropriate CallableStatements,
> > unfortunately.) I can get the count if I don't specify anything else,
> > but I really need the rest of the data as well...
> >
> > I realise this may be an impossible mission, but I thought it would be
> > worth asking.
> >
> > --
> > Jon Skeet - skeet@pobox.com
> > http://www.pobox.com/~skeet

Hi, if you want to make a count of rows is better always use COUNT(1) than
COUNT(*). Because the * implies project all the atributes and the 1 avoid p=
roject the attributes.