postgre

? list all the commands
\l list databases
\conninfo display information about current connection
\c [DBNAME] connect to new database, e.g., \c template1
\dt list tables of the public schema
\dt .* list tables of certain schema, e.g., \dt public.*
\d table-name
Then you can run SQL statements, e.g., SELECT * FROM my_table;(Note: a statement must be terminated with semicolon ;)