Select datatype of the field in postgres

You can get data types from the information_schema (8.4 docs referenced here, but this is not a new feature):

=# select column_name, data_type from information_schema.columns
-# where table_name = 'config';
    column_name     | data_type 
--------------------+-----------
 id                 | integer
 default_printer_id | integer
 master_host_enable | boolean
(3 rows)

run psql -E and then \d student_details

Pulling data type from information_schema is possible, but not convenient (requires joining several columns with a case statement). Alternatively one can use format_type built-in function to do that, but it works on internal type identifiers that are visible in pg_attribute but not in information_schema. Example

SELECT a.attname as column_name, format_type(a.atttypid, a.atttypmod) AS data_type
FROM pg_attribute a JOIN pg_class b ON a.attrelid = b.relfilenode
WHERE a.attnum > 0 -- hide internal columns
AND NOT a.attisdropped -- hide deleted columns
AND b.oid = 'my_table'::regclass::oid; -- example way to find pg_class entry for a table

Based on https://gis.stackexchange.com/a/97834.

https://www.postgresql.org/docs/current/app-psql.html#APP-PSQL-PATTERNS

\gdesc Shows the description (that is, the column names and data types) of the result of the current query buffer. The query is not actually executed; however, if it contains some type of syntax error, that error will be reported in the normal way.

If the current query buffer is empty, the most recently sent query is described instead.

So you can table student_details limit 0 \gdesc Output occupied less space than \d