SELECT
    column_name,
    data_type
FROM
    information_schema.columns
WHERE
    table_name = 'table_name';

with the above query you can retrieve columns and its datatype.

In addition to the command line \d+ <table_name> you already found, you could also use the Information Schema to look up the column data, using information_schema.columns:

SELECT *
  FROM information_schema.columns
 WHERE table_schema = 'your_schema'
   AND table_name   = 'your_table'
     ;

Note: As per the example above, make sure the values are enclosed within quotes.

I don't know why you would ever need to do this, but it is possible using some of the JSON functions introduced in 9.3.

SELECT json_object_keys(row_to_json(t)) FROM
 (SELECT * FROM table1
  LEFT JOIN table2 ON table1.id = table2.tbl1_id LIMIT 1) t;

This will give you the name of every column returned for a single row. Without the LIMIT you would get the columns repeated for every row returned. If you wanted to see the values returned as well you can get more complex:

WITH t as
  (SELECT * FROM table1
   LEFT JOIN table2 ON table1.id = table2.tbl1_id LIMIT 1)
SELECT json_data.key, json_data.value
FROM t, json_each_text(row_to_json(t)) AS json_data;

Both these queries will return all the columns even if they are named the same. If all you want is a list of unique column names, you can utilize hstore:

CREATE EXTENSION hstore; --Create the extension if you need it.

SELECT akeys(hstore(t)) as array_of_columns
FROM
(SELECT * FROM table1
 LEFT JOIN table2 ON table1.id = table2.tbl1id LIMIT 1) t;

Whenever you need to convert user input to identifiers or code in an SQL statement, you need dynamic SQL. Either concatenate the statement in your client an send it to the DB engine or (more efficiently) do it in PL/pgSQL (or some procedural server-side language) dynamically with EXECUTE. More details:

• Refactor a PL/pgSQL function to return the output of various SELECT queries

Solution

CREATE OR REPLACE FUNCTION f_get_columns(_cols text[])
  RETURNS TABLE (col text, val text) AS
$func$
DECLARE
   _col text;
BEGIN
   FOREACH _col IN ARRAY _cols LOOP
      RETURN QUERY EXECUTE
      format('SELECT %1$L::text, %1$I::text FROM tbl t', _col);
   END LOOP;
END
$func$ LANGUAGE plpgsql;

Call:

SELECT * FROM f_array_of_columns('{column1,column2}');

Returns (random values):

col     | val
--------+-----
column1 | 001
column1 | 002
column1 | 003
column2 | {foo,boo,foo}
column2 | {"",for,test}
column2 | {test,foo,boo}

Key elements:

• A matching RETURNS declaration.
• A way to ruturn your results, RETURN QUERY EXECUTE here.
• A FOREACH loop in this particular case.
• format() to simplify string concatenation and escape names and values properly.
  Note the specifiers:
  %1$L ... first parameter as quoted literal.
  %1$I ... first parameter as properly escaped Identifier.

Note how I cast both columns to text (::text) to match the return type and make it work for any data type. Depending on exact requirements, this could be more specific.

With Postgres (and its JDBC driver) you can do the following:

PreparedStatement pstmt = con.prepareStatement("select ... ");
ResultSetMetaData meta = pstmt.getMetaData();
for (int i=1; i <= meta.getColumnCount(); i++)
{
  System.out.println("Column name: " + meta.getColumnName(i) + ", data type: " + meta.getColumnTypeName(i));
}

Note that you do not need to add a where false or limit 0 to the statement. The call to prepareStatement() does not actually execute the query.