A Streamlit app needs a way to find its PostgreSQL database before it can save or retrieve data. A connection string puts the required details in one value: the server address, port, username, password, and database name. The PostgreSQL port is 5432 by default, unless it was changed during installation. section 8.2.5
Connect to a local database
The pattern is `postgresql://<username>:<password>@<server address>:<port>/<database name>`. For a local server, the address can be `localhost`. Put the completed value under `url` in the named connection’s `.streamlit/secrets.toml` entry. Replace the example password with the real one, and do not check `secrets.toml` into Git. section 8.2.5
Listing 8.2 The .streamlit/secrets.toml file
[connections.haikuconn]
url = "postgresql://haiku_lord:password@localhost:5432/haikudb" #1
Shows how a PostgreSQL URL is assigned to `url` under `[connections.haikuconn]`; the password shown is a placeholder. section 8.2.5
The name in that entry must match the name passed to `st.connection("haikuconn", type="sql")`. Once connected, the app can use its database class to run a `SELECT` query and display the returned rows. section 8.2.5
For production, use the connection string supplied by the managed PostgreSQL service instead of the local one. Neon’s Quick Start provides a string with credentials and a hosted server address; its example also includes `sslmode=require`. Keep the string safe. Set up the required tables on the hosted database before expecting the app’s queries to work there. section 8.6.1
