I decided to start doing small “devnotes” on developer stuff I’m doing so I can refer to them later (and also because I feel like I could use more technical content on this blog)
Today is about PostgreSQL. I haven’t used it much beyond standard ANSI sql stuff. You won’t always have a graphical interface to access your database, sometimes you need to ssh to prod and query the database from the shell.
The command line for PostgreSQL is
psql. You can do:
psql [database-user-name] -d [database-name] and it should prompt you for your password.
But when I tried this today, I got:
psql: FATAL: Peer authentication failed for user "[database-user-name]"
The problem had something to do with the permissions available to my ssh user. The workaround was to tell psql I was doing this from the local machine:
psql: FATAL: Peer authentication failed for user "[database-user-name]" -h 127.0.0.1
After connecting, you get a prompt that looks like this:
Now, when I connected today, I had to do some queries, but I wasn’t superfamiliar with the project’s schema, and would have to muck around to find table names and field names. The psql shell provides some handy shortcuts for that:
\dt - outputs a list of tables
\d [table-name] - describes a specific table, showing field names
You can also just directly run an SQL query, just make sure to end it with a semicolon.
If the command outputs a lot of records, it will show them to you in a page-able vim-like format. You can recognize it when it stops with a
: after each page and you can hit spacebar to proceed, and at the end it shows
(END). And like vim, you might not know how to get out of this view. I had to google it myself, you just have to hit
q to go back to the psql shell.