Moved birthdate into separate table.

database/2025_02_08_013647_create_user_birthdates_table.php

@@ -0,0 +1,40 @@
+<?php
+use Index\Db\DbConnection;
+use Index\Db\Migration\DbMigration;
+
+final class CreateUserBirthdatesTable_20250208_013647 implements DbMigration {
+    public function migrate(DbConnection $conn): void {
+        $conn->execute(<<<SQL
+            CREATE TABLE msz_users_birthdates (
+                user_id     INT(10) UNSIGNED NOT NULL,
+                birth_year  SMALLINT(6) NULL DEFAULT NULL,
+                birth_month TINYINT(3) UNSIGNED NOT NULL,
+                birth_day   TINYINT(3) UNSIGNED NOT NULL,
+                PRIMARY KEY (user_id),
+                INDEX users_birthdates_index (birth_month, birth_day),
+                CONSTRAINT users_birthdates_users_foreign
+                    FOREIGN KEY (user_id)
+                    REFERENCES msz_users (user_id)
+                    ON UPDATE CASCADE
+                    ON DELETE CASCADE,
+                CONSTRAINT users_birthdates_ensure_month
+                    CHECK (birth_month BETWEEN 1 AND 12),
+                CONSTRAINT users_birthdates_ensure_day
+                    CHECK (birth_day BETWEEN 1 AND 31)
+            ) ENGINE=InnoDB COLLATE='utf8mb4_bin';
+        SQL);
+
+        $conn->execute(<<<SQL
+            INSERT INTO msz_users_birthdates
+            SELECT user_id, IF(YEAR(user_birthdate) <= 1004, NULL, YEAR(user_birthdate)), MONTH(user_birthdate), DAY(user_birthdate)
+            FROM msz_users
+            WHERE user_birthdate IS NOT NULL
+        SQL);
+
+        $conn->execute(<<<SQL
+            ALTER TABLE msz_users
+                DROP COLUMN user_birthdate,
+                DROP INDEX users_birthdate_index;
+        SQL);
+    }
+}