Refine schema

sql/schema.sql

@@ -1,17 +1,21 @@
+PRAGMA foreign_keys = ON;
+
 CREATE TABLE caster (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
-  code VARCHAR(32) NOT NULL
+  n VARCHAR(32) NOT NULL UNIQUE
 );
 
 CREATE TABLE segment (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
-  title VARCHAR(32) NOT NULL,
-  title_ja VARCHAR(64) NOT NULL
+  n VARCHAR(32) NOT NULL UNIQUE,
+  title VARCHAR(64) NOT NULL UNIQUE
 );
 
 CREATE TABLE schedule (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
-  caster_id INTEGER NOT NULL,
+  caster_id INTEGER,
   segment_id INTEGER NOT NULL,
-  jst DATETIME NOT NULL
+  jst DATETIME NOT NULL UNIQUE,
+  FOREIGN KEY (caster_id) REFERENCES caster (id),
+  FOREIGN KEY (segment_id) REFERENCES segment (id)
 );