Add List Connections To A Database as a postgres til

postgres/list-connections-to-a-database.md

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+# List Connections To A Database
+
+The `pg_stat_activity` table can be used to determine what connections there
+currently are to the PostgreSQL server and to a particular database. To see
+the process ids and usernames of all connection to your PostgreSQL server,
+run the following query:
+
+```sql
+> select pid, usename from pg_stat_activity;
+  pid  |  usename
+-------+------------
+ 57174 | jbranchaud
+ 83420 | jbranchaud
+```
+
+Include `datname` in the requested columns to figure out the database of
+each connection.
+
+```sql
+> select pid, usename, datname from pg_stat_activity;
+  pid  |  usename   |  datname
+-------+------------+-----------
+ 57174 | jbranchaud | hr_hotels
+ 83420 | jbranchaud | pgbyex
+```
+
+The results can be restricted to a particular database as necessary.
+
+```sql
+> select pid, usename from pg_stat_activity where datname = 'hr_hotels';
+  pid  |  usename
+-------+------------
+ 57174 | jbranchaud
+```