Add "table partitioning" chapter

Author: kmoppel

07_table_partitioning.sql

@@ -0,0 +1,48 @@
+\c pg_features_demo
+SET ROLE TO demorole;
+
+/*
+
+When it can be already foreseen that a table will grow huge (100+ GB) or there is for example a "hot data" / "cold data"
+scenario, then it makes sense to think about splitting up the table to so called partitions. And the good thing is that
+starting from v10 there is native support for that - so that users can continue to work with the "main" or "top level"
+table and not care or know about the sub-partitions where data rows are actually living in.
+
+Different partitioning models available:
+
+1) Range based - typically used for having yearly / monthly / weekly partitions.
+2) List based - to explicitly "tell" that rows with specific column(s) values need to go to a specific table
+3) Hash based - for cases where you need X sub-tables evenly filled, but Postgres can choose the exact distribution
+
+
+NB! As of Postgres v12 support for partitioning is almost complete - only automatic creation of sub-partitions and some
+primary key limitations remain, but previous versions had some more limitations so it's recommended to read through the
+documentation before taking them into use on pre v12.
+
+*/
+
+-- the "main" or "parent" table that users will be interacting with
+CREATE TABLE orders (
+    order_nr        int8 NOT NULL ,
+    order_date      timestamptz NOT NULL DEFAULT now()
+    -- data columns ...
+) PARTITION BY RANGE (order_date);
+
+-- partition to hold data for year 2019
+CREATE TABLE orders_y2019 PARTITION OF orders FOR VALUES FROM ('2019-01-01') TO ('2020-01-01');
+
+-- we keep working with the "main" table ...
+INSERT INTO orders
+    SELECT 1;
+
+SELECT * FROM orders; -- 1 row
+
+-- if you want to disable implicit scanning of sub-tables one can use the ONLY keyword
+SELECT * FROM ONLY orders; -- 0 rows
+
+/*
+
+NB! Partition hierarchies can be built many levels deep if needed and mixing different partitioning models - to see the
+whole "tree" one can use the pg_partition_tree() function or for direct descendants of a table use the "psql" \d+ helper
+
+*/