Thread: Question about schema

Hi all,

    Can I use SQL to get info about a table
    which can be gotten by doing a

      \d [table name]

    under psql?


     Rdbms

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If you just want to know what your table looks like, try:

select * from pg_class;

To just get the class names, try select relname from pg_class;

I'm pretty sure that you can execute this from psql c-commands.


-Tony

dbmss@yahoo.com writes:
>     Can I use SQL to get info about a table
>     which can be gotten by doing a
>       \d [table name]
>     under psql?

psql uses plain old SQL queries to extract the info it presents with \d;
it's not doing anything you couldn't do too.  Read the source code for
psql (src/bin/psql/psql.c) to see what queries are used to produce the
various sorts of \d reports.  For example, the particular case of
"\d table" is handled in the routine named tableDesc, and from looking
at that you can see that it constructs a primary query like this:

    SELECT a.attnum, a.attname, t.typname, a.attlen,
    a.atttypmod, a.attnotnull, a.atthasdef
    FROM pg_class c, pg_attribute a, pg_type t
    WHERE c.relname = '<table name here>'
        and a.attnum > 0
        and a.attrelid = c.oid
        and a.atttypid = t.oid
    ORDER BY attnum

Looks like there are additional queries made to get the values of field
defaults and so forth.

All this stuff is kept in the system tables, and you can query those
tables with ordinary queries.

            regards, tom lane