Add List Connections To A Database as a postgres til

README.md

@@ -175,6 +175,7 @@ _340 TILs and counting..._
 - [List All Rows In A Table](postgres/list-all-rows-in-a-table.md)
 - [List All Versions Of A Function](postgres/list-all-versions-of-a-function.md)
 - [List Available Schemas](postgres/list-available-schemas.md)
+- [List Connections To A Database](postgres/list-connections-to-a-database.md)
 - [List Database Users](postgres/list-database-users.md)
 - [Max Identifier Length Is 63 Bytes](postgres/max-identifier-length-is-63-bytes.md)
 - [pg Prefix Is Reserved For System Schemas](postgres/pg-prefix-is-reserved-for-system-schemas.md)

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

@@ -0,0 +1,34 @@
+# 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
+```