diff --git a/pkg/datastore/sqlstore/migrations/mysql/3_referrer_group_column.sql b/pkg/datastore/sqlstore/migrations/mysql/3_referrer_group_column.sql
index 9b19891..f30c11f 100644
--- a/pkg/datastore/sqlstore/migrations/mysql/3_referrer_group_column.sql
+++ b/pkg/datastore/sqlstore/migrations/mysql/3_referrer_group_column.sql
@@ -1,12 +1,16 @@
 -- +migrate Up
 
-ALTER TABLE daily_referrer_stats ADD COLUMN groupname VARCHAR(255) NULL;
+DROP INDEX unique_daily_referrer_stats ON daily_referrer_stats;
+
+ALTER TABLE daily_referrer_stats ADD COLUMN groupname VARCHAR(255);
 ALTER TABLE daily_referrer_stats ADD COLUMN hostname VARCHAR(255);
 ALTER TABLE daily_referrer_stats ADD COLUMN pathname VARCHAR(255);
 
-UPDATE daily_referrer_stats SET hostname = SUBSTRING_INDEX( url, "/", 3) WHERE url != "" ANd hostname = "";
-UPDATE daily_referrer_stats SET pathname = CONCAT("/", SUBSTRING_INDEX( url, "/", -1))  WHERE url != "" AND pathname = "";
 
+UPDATE daily_referrer_stats SET hostname = SUBSTRING_INDEX( url, "/", 3) WHERE url != "" AND ( hostname = "" OR hostname IS NULL);
+UPDATE daily_referrer_stats SET pathname = REPLACE(url, hostname, "") WHERE url != "" AND (pathname = '' OR pathname IS NULL);
+
+CREATE UNIQUE INDEX unique_daily_referrer_stats ON daily_referrer_stats(hostname, pathname, date);
 ALTER TABLE daily_referrer_stats DROP COLUMN url;
 
 -- +migrate Down
diff --git a/pkg/datastore/sqlstore/migrations/postgres/3_referrer_group_column.sql b/pkg/datastore/sqlstore/migrations/postgres/3_referrer_group_column.sql
index b06b5bf..e02cd8a 100644
--- a/pkg/datastore/sqlstore/migrations/postgres/3_referrer_group_column.sql
+++ b/pkg/datastore/sqlstore/migrations/postgres/3_referrer_group_column.sql
@@ -1,13 +1,15 @@
 -- +migrate Up
 
-ALTER TABLE daily_referrer_stats ADD COLUMN groupname VARCHAR(255) NULL;
+ALTER TABLE daily_referrer_stats ADD COLUMN groupname VARCHAR(255);
 ALTER TABLE daily_referrer_stats ADD COLUMN hostname VARCHAR(255);
 ALTER TABLE daily_referrer_stats ADD COLUMN pathname VARCHAR(255);
 
-UPDATE daily_referrer_stats SET hostname = CONCAT( SPLIT_PART(url, '://', 1), '://', SPLIT_PART(SPLIT_PART(url, '://', 2), '/', 1) ) WHERE url != '' AND hostname = '';
-UPDATE daily_referrer_stats SET pathname = SPLIT_PART( url, hostname, 2 ) WHERE url != '' AND pathname = '';
+UPDATE daily_referrer_stats SET hostname = CONCAT( SPLIT_PART(url, '://', 1), '://', SPLIT_PART(SPLIT_PART(url, '://', 2), '/', 1) ) WHERE url != '' AND ( hostname = "" OR hostname IS NULL);
+UPDATE daily_referrer_stats SET pathname = SPLIT_PART( url, hostname, 2 ) WHERE url != '' AND (pathname = '' OR pathname IS NULL);
 
+DROP INDEX IF EXISTS unique_daily_referrer_stats;
 ALTER TABLE daily_referrer_stats DROP COLUMN url;
+CREATE UNIQUE INDEX unique_daily_referrer_stats ON daily_referrer_stats(hostname, pathname, date);
 
 -- +migrate Down
 
diff --git a/pkg/datastore/sqlstore/migrations/sqlite3/3_referrer_group_column.sql b/pkg/datastore/sqlstore/migrations/sqlite3/3_referrer_group_column.sql
index f08b03f..8032120 100644
--- a/pkg/datastore/sqlstore/migrations/sqlite3/3_referrer_group_column.sql
+++ b/pkg/datastore/sqlstore/migrations/sqlite3/3_referrer_group_column.sql
@@ -1,6 +1,6 @@
 -- +migrate Up
 
-ALTER TABLE daily_referrer_stats ADD COLUMN groupname VARCHAR(255) NULL;
+ALTER TABLE daily_referrer_stats ADD COLUMN groupname VARCHAR(255);
 ALTER TABLE daily_referrer_stats ADD COLUMN hostname VARCHAR(255);
 ALTER TABLE daily_referrer_stats ADD COLUMN pathname VARCHAR(255);