Newer versions: (from 8.4 - mentioned in release notes)
Longer but works on all versions:
SELECT * FROM mytablename;
You may wish to use
\x first if it's a wide table, for readability.
For long data:
SELECT * FROM mytable LIMIT 10;
For wide data (big rows), in the
psql command line client, it's useful to use
\x to show the rows in key/value form instead of tabulated, e.g.
\x SELECT * FROM mytable LIMIT 10;
Note that in all cases the semicolon at the end is important.