How to get PostgreSQL to give me MySQL SHOW COLUMNS-like results? - sql

Question

After much mucking about, I'm close (For my sake, I don't care about the type differences). I do, however, want the exact same output format as MySQL. The reason is I'm trying to adapt a MySQL-only tool for use with PostgreSQL. Here's an example output from MySQL (albeit with fewer columns):
mysql> show columns from users;
+-------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(200) | YES | | NULL | |
| institution | varchar(200) | YES | | NULL | |
+-------------+--------------+------+-----+---------+-------+
Here's the table on which I'm testing this:
Table "public.users"
Column | Type | Collation | Nullable | Default
--------------------+------------------------+-----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
name | character varying(255) | | |
role_id | integer | | |
image_url | character varying(510) | | |
institution | character varying(255) | | |
qualifications | text | | |
cv_url | character varying(510) | | |
specializations | text | | |
text_collaboration | text | | |
Indexes:
"users_pkey" PRIMARY KEY, btree (id) Check constraints:
"users_name_not_null" CHECK (name IS NOT NULL) Foreign-key constraints:
"fk_role_id" FOREIGN KEY (role_id) REFERENCES roles(id) Referenced by:
TABLE "novel_reviews" CONSTRAINT "novels_reviewer_id_fkey" FOREIGN KEY (reviewer_id) REFERENCES users(id)
TABLE "review_translations" CONSTRAINT "review_translations_recorder_id_fkey" FOREIGN KEY (recorder_id) REFERENCES users(id)
Here's the query I have... it's probably poorly done esp. with the GROUP BY part:
SELECT column_name AS "Field"
, data_type AS "Type"
, is_nullable AS "Null"
, CASE WHEN is_primary=true THEN 'PRI' ELSE NULL END AS "Key"
, column_default as "Default"
, CASE WHEN column_default LIKE 'nextval(%' THEN 'auto_increment' ELSE '' END AS "Extra"
FROM
(
SELECT c.column_name
, c.data_type
, c.is_nullable
, tc.constraint_type='PRIMARY KEY' AS is_primary
, c.column_default
FROM information_schema.columns AS c
LEFT JOIN information_schema.constraint_column_usage AS ccu USING (column_name, table_name)
LEFT JOIN information_schema.table_constraints tc USING (constraint_name)
WHERE c.table_name = 'users'
GROUP BY c.column_name
, c.data_type
, c.is_nullable
, is_primary
, c.column_default
) as sq;
Here's the results I'm getting currently. Sorry for the poor formatting.
> Field | Type | Null | Key | Default | Extra
> --------------------+-------------------+------+-----+-----------------------------------+----------------
> | cv_url | character varying | YES | |
> | id | integer | NO | | nextval('users_id_seq'::regclass) | auto_increment
> | id | integer | NO | PRI | nextval('users_id_seq'::regclass) | auto_increment
> | image_url | character varying | YES | |
> | institution | character varying | YES | |
> | name | character varying | YES | |
> | qualifications | text | YES | |
> | role_id | integer | YES | |
> | specializations | text | YES | |
> |
> | (10 rows)
I can't figure how to get the second occurrence of id to go away, the one emanating from the non-primarykey constraint. I can't wrap my head around how to drop that. I tried doing WHERE is_primary_key is NULL or is_primary_key=TRUE but that drops the Name field as well, which is joined to a constraint which is also not a primary key.
What I'd like is to get all columns from the table, (each only once) and the string "PRI" if the field is a primary key.
Help! I'm in a bit over my head. Thanks.

Answer 1

It is the query you need :
SELECT *
FROM information_schema.columns
WHERE table_schema = 'public'
AND table_name = 'users'

Answer 2

Figured it out after a lot of banging my head against the wall. First I made a view:
CREATE VIEW table_column_constraints as (SELECT c.table_schema, c.table_name, c.column_name
, c.data_type
, c.is_nullable
, tc.constraint_type
, c.column_default
FROM information_schema.columns AS c
LEFT JOIN information_schema.constraint_column_usage AS ccu USING (column_name, table_name)
LEFT JOIN information_schema.table_constraints tc ON tc.constraint_name=ccu.constraint_name WHERE c.table_schema='public');
Then, I did a de-duplication technique of comparing the table to itself:
SELECT column_name as "Field"
, data_type AS "Type"
, is_nullable AS "Null"
, CASE WHEN constraint_type='PRIMARY KEY' THEN 'PRI' ELSE NULL END AS "Key"
, column_default AS "Default", CASE WHEN column_default LIKE 'nextval(%' THEN 'auto_increment' ELSE '' END AS "Extra"
FROM table_column_constraints as given WHERE given.table_name = 'users'
AND NOT EXISTS (SELECT * FROM table_column_constraints other WHERE other.column_name=given.column_name AND given.constraint_type!='PRIMARY KEY' AND other.constraint_type='PRIMARY KEY');
To get the following results:
Field | Type | Null | Key | Default | Extra
--------------------+-------------------+------+-----+-----------------------------------+----------------
name | character varying | YES | | |
id | integer | NO | PRI | nextval('users_id_seq'::regclass) | auto_increment
image_url | character varying | YES | | |
institution | character varying | YES | | |
qualifications | text | YES | | |
cv_url | character varying | YES | | |
specializations | text | YES | | |
text_collaboration | text | YES | | |
role_id | integer | YES | | |
(9 rows)
I was inspired by https://stackoverflow.com/a/45065229/1151229 on a question called "Selecting rows ordered by some column and distinct on another"