Create unique index on BLSample(containerId, location, subLocation) (#244)

Author: KarlLevik

schemas/ispyb/updates/2024_10_15_BLSample_unique_index.sql

@@ -0,0 +1,16 @@
+-- This update might require some clean-up of the BLSample table in advance to
+-- remove rows that would violate the unique index being created here. Some
+-- example statements that might help:
+--
+-- UPDATE BLSample SET location = NULL WHERE location = '';
+-- UPDATE BLSample SET location = NULL WHERE location = 'null';
+-- UPDATE BLSample SET location = CAST(location AS INT) WHERE location LIKE '0%';
+--
+-- Note that in SQL, NULL != NULL, so therefore you will not violate a unique
+-- index if you have multiple rows where a field used in the index is NULL.
+
+INSERT IGNORE INTO SchemaStatus (scriptName, schemaStatus) VALUES ('2024_10_15_BLSample_unique_index.sql', 'ONGOING');
+
+CREATE UNIQUE INDEX IF NOT EXISTS BLSample_uidx_containerId_location_subLocation ON BLSample(containerId, location, subLocation);
+
+UPDATE SchemaStatus SET schemaStatus = 'DONE' WHERE scriptName = '2024_10_15_BLSample_unique_index.sql';