Index: db-scripts/triggers/uniqueness_and_training_checks.sql
===================================================================
--- db-scripts/triggers/uniqueness_and_training_checks.sql	(revision 42da64dc0d28f9380336816f6fb82c7572d0021d)
+++ db-scripts/triggers/uniqueness_and_training_checks.sql	(revision 42da64dc0d28f9380336816f6fb82c7572d0021d)
@@ -0,0 +1,36 @@
+-- Add useful DB constraints and checks
+
+-- Unique index: ensure a user has at most one daily intake per date
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_indexes WHERE schemaname = 'trekr' AND tablename = 'daily_intakes' AND indexname = 'uq_daily_intake_user_date'
+    ) THEN
+        CREATE UNIQUE INDEX uq_daily_intake_user_date ON trekr.daily_intakes (weight_user_id, date);
+    END IF;
+END$$;
+
+-- Prevent inserting training sessions with future date
+CREATE OR REPLACE FUNCTION trekr.fn_check_training_date()
+RETURNS trigger LANGUAGE plpgsql AS $$
+BEGIN
+    IF NEW.date > current_date THEN
+        RAISE EXCEPTION 'Training session date cannot be in the future: %', NEW.date;
+    END IF;
+    RETURN NEW;
+END$$;
+
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_trigger t
+        JOIN pg_class c ON t.tgrelid = c.oid
+        WHERE t.tgname = 'trg_check_training_date' AND c.relname = 'training_sessions'
+    ) THEN
+        CREATE TRIGGER trg_check_training_date
+        BEFORE INSERT OR UPDATE ON trekr.training_sessions
+        FOR EACH ROW
+        EXECUTE FUNCTION trekr.fn_check_training_date();
+    END IF;
+END$$;
+