List databases / schemas

Oracle

-- Schemas (users):
SELECT username FROM dba_users ORDER BY username;
-- Multitenant (CDB) PDBs:
SELECT name, open_mode FROM v$pdbs;

In Oracle a 'database' corresponds to the instance; the separation is at the schema (user) level or the PDB level inside a CDB.

PostgreSQL

SELECT datname FROM pg_database WHERE datistemplate = false;
-- psql shortcut: \l

For schemas: SELECT schema_name FROM information_schema.schemata;

MySQL

SHOW DATABASES;

In MySQL, 'database' and 'schema' are synonyms.

SQL Server

SELECT name, state_desc FROM sys.databases ORDER BY name;

state_desc shows the database state, such as ONLINE/OFFLINE/RESTORING.

MongoDB

show dbs
// or: db.adminCommand({ listDatabases: 1 })

Empty databases (no data written yet) do not appear in the list.

Redis

INFO keyspace
# db0:keys=..., db1:keys=... lines show the logical DBs in use

Redis has numbered logical DBs (default 0-15); in Cluster mode only DB 0 is used.