Re: Re: PostreSQL SQL for MySQL SQL

On 6 Feb 2001, at 14:24, Chuck Esterbrook wrote:

> At 01:10 PM 2/6/2001 -0600, John Burski wrote:
> >interactively, via psql, via the Perl Pg module, or via PHP.  If you
> >attempt to drop a database that doesn't exist, PostgreSQL will issue an
> >error message.  If you're running interactively, you'll see the message;
> >if you're accessing via a Perl module or PHP, you can check the query
> >results to see if an error occurred.  I'm fairly certain that this same
> >mechanism exists if you're using C or C++ to access your databases.
>
> I'd prefer to skip the error message, because otherwise my regression test
> suite will barf, saying something like "Test X failed due to SQL error". I
> suppose I work in some code to catch this and swallow it.
>
You can always search the system catalog to know if a DB exists
or not.

This is how I do it using pglib, in C:

 sprintf(Query,"SELECT * from pg_database where
datname='%s';",DBname);
        res = PQexec(conn, Query);
        if (PQresultStatus(res) != PGRES_TUPLES_OK)
                Throw_Error(121);
        NumMax=PQntuples(res);

        if(NumMax==1)
        {
        sprintf(Query,"DROP DATABASE %s;",DBname);
        res = PQexec(conn, Query);
        if (PQresultStatus(res) != PGRES_COMMAND_OK)
                Throw_Error(122);
        }

> >I'm not familiar with the "use Foo" functionality of MySQL, so I can't
> >discuss it.
>
> I think you may have answered it with your "\connect dbname" comment.
> Provided that I can put that after the "create database" in the SQL script
> and feed the whole mess to psql.
>

Sure you can. If you use psql as command interpreter, "\connect
dbname" has almost 1:1 functionality in respect to MySql's "use
foo". If you use a pglib-based API (i.e. you're using C, Perl, PHP or
other) you got to use the connection function to select the db.

HTH, bye!


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