From df47fc3d7da1bd74e165df6f37269b0b8ce2d446 Mon Sep 17 00:00:00 2001
From: Michele Cereda <cereda.michele@gmail.com>
Date: Fri, 1 Nov 2024 20:56:26 +0100
Subject: [PATCH] chore(postgresql): dump acquired knowledge

---
 knowledge base/postgresql.md    | 15 +++++++----
 snippets/postgres/commands.sh   | 20 ++++++++++++++
 snippets/postgres/functions.sql | 47 ++++++++++++++++++++-------------
 snippets/postgres/primer.sql    | 46 ++++++++++++++++++++++++++++++--
 4 files changed, 102 insertions(+), 26 deletions(-)

diff --git a/knowledge base/postgresql.md b/knowledge base/postgresql.md
index 3b9623f..0761579 100644
--- a/knowledge base/postgresql.md	
+++ b/knowledge base/postgresql.md	
@@ -47,11 +47,12 @@ EOF
 chmod '600' ~/'.pgpass'
 
 # Set up the per-user services file.
+# do *not* use spaces around the '=' sign.
 cat <<EOF > ~/'.pg_service.conf'
 [prod]
-host = prod.0123456789ab.eu-west-1.rds.amazonaws.com
-port = 5433
-user = master
+host=prod.0123456789ab.eu-west-1.rds.amazonaws.com
+port=5433
+user=master
 EOF
 ```
 
@@ -137,7 +138,7 @@ CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer
 AS $$
   BEGIN
     RETURN i + 1;
-  END
+  END;
 $$
 LANGUAGE plpgsql;
 ```
@@ -153,7 +154,7 @@ AS $func$
   BEGIN
     EXECUTE format('SELECT count(%s) FROM %s LIMIT 2', column_name, table_name) INTO result;
     RETURN result;
-  END
+  END;
 $func$;
 SELECT * FROM entries_in_column('vendors','vendor_id');
 ```
@@ -234,6 +235,8 @@ psql -h 'localhost' -p '6543' -U 'postgres' -d 'postgres' -W
 - [How to write update function (stored procedure) in Postgresql?]
 - [How to search a specific value in all tables (PostgreSQL)?]
 - [PostgreSQL: Show all the privileges for a concrete user]
+- [PostgreSQL - disabling constraints]
+- [Hashing a String to a Numeric Value in PostgreSQL]
 
 <!--
   Reference
@@ -257,11 +260,13 @@ psql -h 'localhost' -p '6543' -U 'postgres' -d 'postgres' -W
 [connect to a postgresql database]: https://www.postgresqltutorial.com/connect-to-postgresql-database/
 [dverite/postgresql-functions]: https://github.com/dverite/postgresql-functions
 [get count of records affected by insert or update in postgresql]: https://stackoverflow.com/questions/4038616/get-count-of-records-affected-by-insert-or-update-in-postgresql#78459743
+[hashing a string to a numeric value in postgresql]: https://stackoverflow.com/questions/9809381/hashing-a-string-to-a-numeric-value-in-postgresql#69650940
 [how to generate scram-sha-256 to create postgres 13 user]: https://stackoverflow.com/questions/68400120/how-to-generate-scram-sha-256-to-create-postgres-13-user
 [how to scram in postgres with pgbouncer]: https://www.crunchydata.com/blog/pgbouncer-scram-authentication-postgresql
 [how to search a specific value in all tables (postgresql)?]: https://stackoverflow.com/questions/5350088/how-to-search-a-specific-value-in-all-tables-postgresql/23036421#23036421
 [how to write update function (stored procedure) in postgresql?]: https://stackoverflow.com/questions/21087710/how-to-write-update-function-stored-procedure-in-postgresql
 [pgxn-manager]: https://github.com/pgxn/pgxn-manager
+[postgresql - disabling constraints]: https://stackoverflow.com/questions/2679854/postgresql-disabling-constraints#2681413
 [postgresql_anonymizer]: https://postgresql-anonymizer.readthedocs.io/en/stable/
 [postgresql: get member roles and permissions]: https://www.cybertec-postgresql.com/en/postgresql-get-member-roles-and-permissions/
 [postgresql: show all the privileges for a concrete user]: https://stackoverflow.com/questions/40759177/postgresql-show-all-the-privileges-for-a-concrete-user
diff --git a/snippets/postgres/commands.sh b/snippets/postgres/commands.sh
index 2bcb551..7081794 100644
--- a/snippets/postgres/commands.sh
+++ b/snippets/postgres/commands.sh
@@ -17,6 +17,25 @@ docker run -d --name 'pgadmin' \
 	-e 'PGADMIN_DEFAULT_PASSWORD=password' \
 	'dpage/pgadmin4'
 
+
+# Set up the credentials file
+# Format => hostname:port:database:username:password
+# Supports wildcards
+cat <<EOF > ~/'.pgpass'
+postgres.lan:5643:postgres:postgres:BananaORama
+*:*:sales:elaine:modestPassword
+EOF
+chmod '600' ~/'.pgpass'
+
+# Set up the per-user services file.
+# do *not* use spaces around the '=' sign.
+cat <<EOF > ~/'.pg_service.conf'
+[prod]
+host=prod.0123456789ab.eu-west-1.rds.amazonaws.com
+port=5433
+user=master
+EOF
+
 # Connect to DBs
 psql 'postgres'
 psql 'postgres' 'admin'
@@ -24,6 +43,7 @@ psql --host 'prod.db.lan' --port '5432' --username 'postgres' --database 'postgr
 psql -h 'host.fqnd' -p '5432' -U 'admin' -d 'postgres' -W
 psql 'postgresql://localhost:5433/games?sslmode=require'
 psql 'host=host.fqdn port=5467 user=admin dbname=postgres'
+psql "service=prod sslmode=require"
 
 # List available databases
 psql … --list
diff --git a/snippets/postgres/functions.sql b/snippets/postgres/functions.sql
index 064846a..e9bb740 100644
--- a/snippets/postgres/functions.sql
+++ b/snippets/postgres/functions.sql
@@ -23,25 +23,34 @@ LANGUAGE plpgsql
 AS $$
   DECLARE affected_rows INTEGER;
   BEGIN
-    EXECUTE format('
-      WITH
-        ctids AS (
-          SELECT
-            ROW_NUMBER() OVER (),
-            ctid
-          FROM %I
-        ),
-        shuffled_values AS (
-          SELECT
-            ROW_NUMBER() OVER (ORDER BY RANDOM()),
-            %I AS new_value
-          FROM %I
-        )
-      UPDATE %I
-        SET %I = shuffled_values.new_value
-        FROM shuffled_values JOIN ctids ON shuffled_values.row_number = ctids.row_number
-        WHERE %I.ctid = ctids.ctid
-    ', table_name, column_name, table_name, table_name, column_name, table_name);
+    SET CONSTRAINTS ALL DEFERRED;
+    EXECUTE format(
+      '
+        WITH
+          ctids AS (
+            SELECT
+              ROW_NUMBER() OVER (),
+              ctid
+            FROM %I
+          ),
+          shuffled_values AS (
+            SELECT
+              ROW_NUMBER() OVER (ORDER BY RANDOM()),
+              %I AS new_value
+            FROM %I
+          )
+        UPDATE %I
+          SET %I = shuffled_values.new_value
+          FROM shuffled_values JOIN ctids ON shuffled_values.row_number = ctids.row_number
+          WHERE %I.ctid = ctids.ctid
+      ',
+      table_name,
+      column_name,
+      table_name,
+      table_name,
+      column_name,
+      table_name
+    );
     GET DIAGNOSTICS affected_rows = ROW_COUNT;
     RETURN affected_rows;
   END;
diff --git a/snippets/postgres/primer.sql b/snippets/postgres/primer.sql
index 9ba1be9..c157785 100644
--- a/snippets/postgres/primer.sql
+++ b/snippets/postgres/primer.sql
@@ -85,6 +85,7 @@ CREATE TABLE people (
 );
 
 -- Show table structure
+-- Includes constraints
 \d sales
 \d+ clients
 SELECT column_name, data_type, character_maximum_length FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = 'vendors';
@@ -290,11 +291,20 @@ SELECT setseed(0.25), round(random()::DECIMAL, 15) AS random_number;  -- seed mu
 -- Refer <https://www.postgresql.org/docs/current/sql-createfunction.html>
 \df
 \df+ to_char
+\df+ hash*
 SELECT routine_name FROM information_schema.routines WHERE routine_type = 'FUNCTION';
 SELECT p.proname FROM pg_catalog.pg_namespace n JOIN pg_catalog.pg_proc p ON p.pronamespace = n.oid WHERE p.prokind = 'f';
 
 CREATE OR REPLACE FUNCTION return_1() RETURNS INTEGER LANGUAGE SQL RETURN 1;
 
+-- Show functions definition
+\sf hash_numeric
+\sf+ hashfloat8
+
+-- Given hash_national_ids(country TEXT, table_name TEXT, column_name DEFAULT 'national_id')
+SELECT hash_national_ids('estonia', 'clients');
+SELECT hash_national_ids(country => 'estonia', table_name => 'clients', column_name => 'national_id');
+
 
 -- Type casting
 SELECT pg_typeof(10);
@@ -382,7 +392,20 @@ ALTER TABLE signups RENAME CONSTRAINT signups_customer_id_fkey TO something_blue
 ALTER TABLE vendors SET CONSTRAINT vendors_value_uindex DEFERRED;
 
 
--- Show all constraints
+-- Show all constraints in the current DB
+SELECT
+  ns.nspname AS schema,
+  class.relname AS "table",
+  con.conname AS "constraint",
+  con.contype AS "type",
+  con.condeferrable AS "deferrable",
+  con.condeferred AS "deferred"
+FROM pg_constraint con
+  INNER JOIN pg_class class ON class.oid = con.conrelid
+  INNER JOIN pg_namespace ns ON ns.oid = class.relnamespace
+WHERE ns.nspname != 'pg_catalog'
+ORDER BY 1, 2, 3;
+-- Show all uniqueness constraints in the current DB
 SELECT
   ns.nspname AS schema,
   class.relname AS "table",
@@ -393,6 +416,25 @@ FROM pg_constraint con
   INNER JOIN pg_class class ON class.oid = con.conrelid
   INNER JOIN pg_namespace ns ON ns.oid = class.relnamespace
 WHERE
-  con.contype IN ('p', 'u') AND
+  con.contype IN ('u') AND
   ns.nspname != 'pg_catalog'
 ORDER BY 1, 2, 3;
+
+
+-- List all uniqueness constraints in a schema
+SELECT
+  class.relname AS "table",
+  con.conname AS "constraint",
+  con.condeferrable AS "deferrable",
+  con.condeferred AS "deferred"
+FROM pg_constraint con
+  INNER JOIN pg_class class ON class.oid = con.conrelid
+  INNER JOIN pg_namespace ns ON ns.oid = class.relnamespace
+WHERE
+  con.contype IN ('u') AND
+  ns.nspname = 'public'
+ORDER BY 1, 2, 3;
+
+
+-- Empty tables of their data
+TRUNCATE TABLE sales;