test: 补充测试数据库初始化脚本的注释

src/test/resources/init_tables.sql

@@ -1,3 +1,4 @@
+-- 测试用户表，覆盖全部列类型（数值/字符串/布尔/时间），用于验证 RowMapper 和查询功能
 DROP TABLE IF EXISTS users;
 
 CREATE TABLE users (
@@ -12,19 +13,25 @@ CREATE TABLE users (
     work_start_time TIME
 );
 
+-- 唯一约束用于测试 batchUpdate 的重复键错误场景
 ALTER TABLE users ADD CONSTRAINT uk_username UNIQUE (username);
 
+-- 完整数据行（全部字段非空）
 INSERT INTO users (username, email, age, balance, active, created_at, birth_date, work_start_time)
 VALUES ('alice', 'alice@example.com', 28, 15000, TRUE, '2024-01-15 09:30:00', '1996-05-20', '08:00:00');
 
+-- 完整数据行
 INSERT INTO users (username, email, age, balance, active, created_at, birth_date, work_start_time)
 VALUES ('bob', 'bob@example.com', 35, 25000, TRUE, '2023-11-01 14:00:00', '1989-03-12', '09:30:00');
 
+-- null 数据行：email、age、birth_date、work_start_time 均为 null，用于测试空字段映射
 INSERT INTO users (username, email, age, balance, active, created_at, birth_date, work_start_time)
 VALUES ('charlie', NULL, NULL, 5000, FALSE, '2025-03-10 11:15:00', NULL, NULL);
 
+-- 部分 null 数据行：balance 为 null，created_at 为 null，用于测试字段级 null 映射
 INSERT INTO users (username, email, age, balance, active, created_at, birth_date, work_start_time)
 VALUES ('diana', 'diana@example.com', 42, NULL, TRUE, NULL, '1982-11-08', '07:45:00');
 
+-- 完整数据行
 INSERT INTO users (username, email, age, balance, active, created_at, birth_date, work_start_time)
 VALUES ('eve', 'eve@example.com', 31, 8000, TRUE, '2024-07-22 16:45:00', '1993-01-30', '10:00:00');