schema: set cat_id in ttrss_feeds to null when category is deleted

schema/ttrss_schema_mysql.sql

@@ -80,7 +80,7 @@ create table ttrss_feeds (id integer not null auto_increment primary key,
 	index(owner_uid),
 	foreign key (owner_uid) references ttrss_users(id) ON DELETE CASCADE,
 	index(cat_id),
-	foreign key (cat_id) references ttrss_feed_categories(id),
+	foreign key (cat_id) references ttrss_feed_categories(id) ON DELETE SET NULL,
 	index(parent_feed),
 	foreign key (parent_feed) references ttrss_feeds(id) ON DELETE SET NULL) TYPE=InnoDB;
 

schema/ttrss_schema_pgsql.sql

@@ -52,7 +52,7 @@ create table ttrss_feed_categories(id serial not null primary key,
 create table ttrss_feeds (id serial not null primary key,
 	owner_uid integer not null references ttrss_users(id) on delete cascade,
 	title varchar(200) not null, 
-	cat_id integer references ttrss_feed_categories(id) default null,
+	cat_id integer default null references ttrss_feed_categories(id) on delete set null,
 	feed_url varchar(250) not null, 
 	icon_url varchar(250) not null default '',
 	update_interval integer not null default 0,