From da3b155ae85af2b6eb889b0c712723b40eb94378 Mon Sep 17 00:00:00 2001
From: poveyd <32199157+poveyd@users.noreply.github.com>
Date: Mon, 4 May 2020 12:18:25 +0100
Subject: [PATCH] Create cycle_notification_history_in_batches.sql

---
 .../cycle_notification_history_in_batches.sql | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 database_maintenance/cycle_notification_history_in_batches.sql

diff --git a/database_maintenance/cycle_notification_history_in_batches.sql b/database_maintenance/cycle_notification_history_in_batches.sql
new file mode 100644
index 000000000..82297434f
--- /dev/null
+++ b/database_maintenance/cycle_notification_history_in_batches.sql
@@ -0,0 +1,31 @@
+-- Call once at the start of the process
+
+CREATE TABLE notification_history_pivot AS SELECT * from notification_history WHERE 1=2;
+
+SELECT id
+INTO nh_temp
+FROM notification_history;
+
+SELECT COUNT(*) AS 'Total number of rows in nh' FROM nh_temp;
+
+DELETE FROM nh_temp t
+USING notification_history_pivot p
+WHERE t.id = p.id;
+
+SELECT COUNT(*) AS 'Number of rows remaining that need moving across from nh to nh_pivot' FROM nh_temp;
+
+-- In each function call, using same database connection as used for the above SQL (needs to be in a transaction; this can be inside a stored function or in a transaction from the code)
+
+INSERT INTO notification_history_pivot
+SELECT n.*
+FROM notification_history n,
+     nh_temp t
+WHERE n.id = t.id;
+
+DELETE FROM nh_temp t
+USING notification_history_pivot p
+WHERE t.id = p.id;
+
+SELECT COUNT(*) from nh_temp;
+
+-- Loop until this result is zero.