well it is a postgres database 
docker-compose exec db bash
bash-5.0# psql --dbname=mattermost --username=mmuser --password
mattermost=# \d users
Table "public.users"
Column | Type | Modifiers
--------------------------+-------------------------+---------------------------------------------------------------------------------------------------------
id | character varying(26) | not null
createat | bigint |
updateat | bigint |
deleteat | bigint |
username | character varying(64) |
password | character varying(128) |
authdata | character varying(128) |
authservice | character varying(32) |
email | character varying(128) |
emailverified | boolean |
nickname | character varying(64) |
firstname | character varying(64) |
lastname | character varying(64) |
position | character varying(128) |
roles | character varying(256) |
allowmarketing | boolean |
props | character varying(4000) |
notifyprops | character varying(2000) |
lastpasswordupdate | bigint |
lastpictureupdate | bigint |
failedattempts | integer |
locale | character varying(5) |
mfaactive | boolean |
mfasecret | character varying(128) |
timezone | character varying(256) | default '{"automaticTimezone":"","manualTimezone":"","useAutomaticTimezone":"true"}'::character varying
acceptedtermsofserviceid | character varying(64) | default ''::character varying
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
"users_authdata_key" UNIQUE CONSTRAINT, btree (authdata)
"users_email_key" UNIQUE CONSTRAINT, btree (email)
"users_username_key" UNIQUE CONSTRAINT, btree (username)
"idx_users_all_no_full_name_txt" gin (to_tsvector('english'::regconfig, (((username::text || ' '::text) || nickname::text) || ' '::text) || email::text))
"idx_users_all_txt" gin (to_tsvector('english'::regconfig, (((((((username::text || ' '::text) || firstname::text) || ' '::text) || lastname::text) || ' '::text) || nickname::text) || ' '::text) || email::text))
"idx_users_create_at" btree (createat)
"idx_users_delete_at" btree (deleteat)
"idx_users_email" btree (email)
"idx_users_email_lower_textpattern" btree (lower(email::text) text_pattern_ops)
"idx_users_firstname_lower_textpattern" btree (lower(firstname::text) text_pattern_ops)
"idx_users_lastname_lower_textpattern" btree (lower(lastname::text) text_pattern_ops)
"idx_users_names_no_full_name_txt" gin (to_tsvector('english'::regconfig, (username::text || ' '::text) || nickname::text))
"idx_users_names_txt" gin (to_tsvector('english'::regconfig, (((((username::text || ' '::text) || firstname::text) || ' '::text) || lastname::text) || ' '::text) || nickname::text))
"idx_users_nickname_lower_textpattern" btree (lower(nickname::text) text_pattern_ops)
"idx_users_update_at" btree (updateat)
"idx_users_username_lower_textpattern" btree (lower(username::text) text_pattern_ops)