Add Show The Hidden Queries Behind Backslash Commands as a Postgres TIL

postgres/show-the-hidden-queries-behind-backslash-commands.md

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+# Show The Hidden Queries Behind Backslash Commands
+
+The `ECHO_HIDDEN` variable in PostgreSQL's `psql` determines whether the
+queries behind backslash commands are displayed. It defaults to `false`. So,
+generally, when you run something like `\d` or `\l+`, you'll just see the
+result and not the query that helped produce it.
+
+If you're curious what's behind any of these backslash commands, then set
+`ECHO_HIDDEN` to `true` to get a look.
+
+```sql
+> \set ECHO_HIDDEN true
+> \d
+********* QUERY **********
+SELECT n.nspname as "Schema",
+  c.relname as "Name",
+  CASE c.relkind WHEN 'r' THEN 'table' WHEN 'v' THEN 'view' WHEN 'm' THEN 'materialized view' WHEN 'i' THEN 'index' WHEN 'S' THEN 'sequence' WHEN 's' THEN 'special' WHEN 'f' THEN 'foreign table' WHEN 'p' THEN 'partitioned table' WHEN 'I' THEN 'partitioned index' END as "Type",
+  pg_catalog.pg_get_userbyid(c.relowner) as "Owner"
+FROM pg_catalog.pg_class c
+     LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
+WHERE c.relkind IN ('r','p','v','m','S','f','')
+      AND n.nspname <> 'pg_catalog'
+      AND n.nspname <> 'information_schema'
+      AND n.nspname !~ '^pg_toast'
+  AND pg_catalog.pg_table_is_visible(c.oid)
+ORDER BY 1,2;
+**************************
+
+               List of relations
+ Schema |     Name     |   Type   |   Owner
+--------+--------------+----------+------------
+ public | users        | table    | jbranchaud
+ public | users_id_seq | sequence | jbranchaud
+```
+
+That query is what `psql` uses to list the relations for your current database.