chore(postgres): dump acquired knowledge

snippets/postgres/functions.sql

@@ -0,0 +1,54 @@
+/**
+ * Shuffle values in a column
+ * Returns the number of affected rows
+ *
+ * Only works on that column, with no regards for data connections.
+ * Requires a way to identify the row in the source table during the update.
+ * └── Using 'ctid' over a table's primary key to avoid the need of specifying another column.
+ * ctids shall stay the same, but values shall be numbered randomly (hence the shuffling part).
+ *
+ * Credits to <https://stackoverflow.com/questions/33555524/postgresql-shuffle-column-values#33555639>.
+ *
+ * SELECT user_id, name FROM band_members WHERE name IN ('mark', 'tom', 'travis') ORDER BY name;
+ * SELECT shuffle_column('band_members','name');
+ * SELECT user_id, name FROM band_members WHERE name IN ('mark', 'tom', 'travis') ORDER BY name;
+ **/
+
+CREATE OR REPLACE FUNCTION shuffle_column(
+  table_name TEXT,
+  column_name TEXT
+)
+RETURNS INTEGER
+LANGUAGE plpgsql
+AS $$
+  DECLARE affected_rows INTEGER;
+  BEGIN
+    EXECUTE format('
+      WITH
+        ctids AS (
+          SELECT
+            ROW_NUMBER() OVER (),
+            ctid
+          FROM %I
+        ),
+        shuffled_values AS (
+          SELECT
+            ROW_NUMBER() OVER (ORDER BY RANDOM()),
+            %I AS new_value
+          FROM %I
+        )
+      UPDATE %I
+        SET %I = shuffled_values.new_value
+        FROM shuffled_values JOIN ctids ON shuffled_values.row_number = ctids.row_number
+        WHERE %I.ctid = ctids.ctid
+    ', table_name, column_name, table_name, table_name, column_name, table_name);
+    GET DIAGNOSTICS affected_rows = ROW_COUNT;
+    RETURN affected_rows;
+  END;
+$$;
+
+
+/**
+ * Replace UUID in a column
+ * Returns the number of affected rows
+ **/