horse, mdb: put skill groups in skills

Fixes #13.

mdb/sql/skill-group-skills.sql

@@ -0,0 +1,43 @@
+WITH g AS (
+	SELECT
+		l.id AS l,
+		r.id AS r,
+		r.group_rate,
+		r.rarity
+	FROM skill_data l
+		JOIN skill_data r ON l.group_id = r.group_id
+	
+	UNION ALL
+
+	SELECT
+		s.id AS l,
+		i.id AS r,
+		i.group_rate,
+		i.rarity
+	FROM skill_data s
+		JOIN skill_data i ON s.id IN (i.unique_skill_id_1, i.unique_skill_id_2)
+	
+	UNION ALL
+
+	SELECT
+		s.id AS l,
+		i.id AS r,
+		i.group_rate,
+		i.rarity
+	FROM skill_data s
+		JOIN skill_data i ON i.id IN (s.unique_skill_id_1, s.unique_skill_id_2)
+
+	UNION ALL
+
+	SELECT
+		l.id AS l,
+		r.id AS r,
+		r.group_rate,
+		r.rarity
+	FROM skill_data i
+		JOIN skill_data l ON l.id IN (i.unique_skill_id_1, i.unique_skill_id_2)
+		JOIN skill_data r ON r.id IN (i.unique_skill_id_1, i.unique_skill_id_2)
+	WHERE l.id != r.id
+)
+SELECT * FROM g
+ORDER BY l, group_rate, rarity DESC