I got asked this: having this table:
# SELECT * FROM a ORDER BY d; t | d ---+---- O | 1 O | 2 O | 3 M | 4 M | 5 M | 6 M | 7 O | 8 O | 9 O | 10 I | 11 I | 12 I | 13 (13 ROWS)
Is it possible to add “rank" column, that will increment whenever t changed?
Let's assume you have very simple table with users:
# \d users
Table "public.users"
Column | Type | Modifiers
-----------+---------+----------------------------------------------------
id | integer | not null default nextval('users_id_seq'::regclass)
username | text | not null
is_active | boolean | not null default true
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
"users_username_key" UNIQUE, btree (username)And you'd like to count all users, and know how many of them are active …
Continue reading Tips N' Tricks – count of all and just some