Select datatype of the field in postgres
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23-09-2019 - |
Question
How do I get datatype of specific field from table in postgres ? For example I have the following table, student_details ( stu_id integer, stu_name varchar(30 ), joined_date timestamp );
In this using the field name / or any other way, I need to get the datatype of the specific field. Is there any possibility ?
No correct solution
OTHER TIPS
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)
You can use the pg_typeof() function, which also works well for arbitrary values.
SELECT pg_typeof("stu_id"), pg_typeof(100) from student_details limit 1;
run psql -E
and then \d student_details
Try this request :
SELECT column_name, data_type FROM information_schema.columns WHERE
table_name = 'YOUR_TABLE' AND column_name = 'YOUR_FIELD';
If you like 'Mike Sherrill' solution but don't want to use psql, I used this query to get the missing information:
select column_name,
case
when domain_name is not null then domain_name
when data_type='character varying' THEN 'varchar('||character_maximum_length||')'
when data_type='numeric' THEN 'numeric('||numeric_precision||','||numeric_scale||')'
else data_type
end as myType
from information_schema.columns
where table_name='test'
with result:
column_name | myType
-------------+-------------------
test_id | test_domain
test_vc | varchar(15)
test_n | numeric(15,3)
big_n | bigint
ip_addr | inet
The information schema views and pg_typeof() return incomplete type information. Of these answers, psql
gives the most precise type information. (The OP might not need such precise information, but should know the limitations.)
create domain test_domain as varchar(15);
create table test (
test_id test_domain,
test_vc varchar(15),
test_n numeric(15, 3),
big_n bigint,
ip_addr inet
);
Using psql
and \d public.test
correctly shows the use of the data type test_domain
, the length of varchar(n) columns, and the precision and scale of numeric(p, s) columns.
sandbox=# \d public.test Table "public.test" Column | Type | Modifiers ---------+-----------------------+----------- test_id | test_domain | test_vc | character varying(15) | test_n | numeric(15,3) | big_n | bigint | ip_addr | inet |
This query against an information_schema view does not show the use of test_domain
at all. It also doesn't report the details of varchar(n) and numeric(p, s) columns.
select column_name, data_type
from information_schema.columns
where table_catalog = 'sandbox'
and table_schema = 'public'
and table_name = 'test';
column_name | data_type -------------+------------------- test_id | character varying test_vc | character varying test_n | numeric big_n | bigint ip_addr | inet
You might be able to get all that information by joining other information_schema views, or by querying the system tables directly. psql -E
might help with that.
The function pg_typeof()
correctly shows the use of test_domain
, but doesn't report the details of varchar(n) and numeric(p, s) columns.
select pg_typeof(test_id) as test_id,
pg_typeof(test_vc) as test_vc,
pg_typeof(test_n) as test_n,
pg_typeof(big_n) as big_n,
pg_typeof(ip_addr) as ip_addr
from test;
test_id | test_vc | test_n | big_n | ip_addr -------------+-------------------+---------+--------+--------- test_domain | character varying | numeric | bigint | inet
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.