feat: add MySQL database support alongside SQL Server

This commit implements multi-database support, allowing the system to switch
between SQL Server and MySQL databases seamlessly.

## New Features
- Database type selection (SQL Server or MySQL) via configuration
- Automatic table name conversion between formats ([dbo].[table] → dbo_table)
- Automatic parameter placeholder handling (? for SQL Server, %s for MySQL)
- GUI settings tab now includes database type dropdown and MySQL configuration

## Database Abstraction Layer
- db/base_connection.py: Abstract base class for database connections
- db/sqlserver_connection.py: SQL Server implementation
- db/mysql_connection.py: MySQL implementation using mysql-connector-python
- db/connection_factory.py: Factory pattern for creating connections
- db/table_name_converter.py: Table name format conversion utility

## DAO Base Class
- db/base_dao.py: Base DAO with helper methods for SQL conversion and placeholders

## Updated Components
- config/schema.py: Extended with DatabaseType enum and MySQL/SQLServer config classes
- config/defaults.py: Added MySQL default configuration
- config/loader.py: Updated to handle new database structure
- db/connection.py: Refactored to use factory pattern and load user config
- All DAO files: Updated to inherit from BaseDAO with automatic conversion

## Dependencies
- Added mysql-connector-python>=8.0.0 to requirements.txt

## Configuration
To use MySQL, set db_type to "mysql" in config/user_settings.json:
{
  "database": {
    "db_type": "mysql",
    "mysql": {
      "host": "192.168.31.83",
      "port": 3306,
      "database": "BLD_DB",
      "username": "remote_user",
      "password": "3.1415926Beeke"
    }
  }
}

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

db/table_name_converter.py

@@ -0,0 +1,140 @@
+"""
+表名转换工具
+
+处理 SQL Server 和 MySQL 之间的表名格式转换
+"""
+
+import re
+from typing import List
+
+
+class TableNameConverter:
+    """表名转换工具类"""
+
+    # 匹配 SQL Server 表名格式：[schema].[tablename] 或 [schema].[table name]
+    SQLSERVER_PATTERN = re.compile(r'\[([^\]]+)\]\.\[([^\]]+)\]')
+
+    @staticmethod
+    def to_mysql(table_name: str) -> str:
+        """
+        将 SQL Server 表名格式转换为 MySQL 格式
+
+        SQL Server: [schema].[tablename] → MySQL: schema_tablename
+        SQL Server: tablename → MySQL: dbo_tablename (默认 dbo)
+
+        Args:
+            table_name: SQL Server 格式的表名
+
+        Returns:
+            MySQL 格式的表名
+
+        Examples:
+            >>> TableNameConverter.to_mysql('[dbo].[BIPUsers]')
+            'dbo_BIPUsers'
+            >>> TableNameConverter.to_mysql('DiscreteMaterialPlanData')
+            'dbo_DiscreteMaterialPlanData'
+            >>> TableNameConverter.to_mysql('[productionContractData].[26年压力表合同数据]')
+            'productionContractData_26年压力表合同数据'
+        """
+        # 尝试匹配 [schema].[tablename] 格式
+        match = TableNameConverter.SQLSERVER_PATTERN.match(table_name.strip())
+        if match:
+            schema = match.group(1)
+            table = match.group(2)
+            return f"{schema}_{table}"
+
+        # 如果没有匹配到，使用默认 schema dbo
+        return f"dbo_{table_name}"
+
+    @staticmethod
+    def to_sqlserver(table_name: str) -> str:
+        """
+        将 MySQL 表名格式转换为 SQL Server 格式
+
+        MySQL: schema_tablename → SQL Server: [schema].[tablename]
+
+        Args:
+            table_name: MySQL 格式的表名
+
+        Returns:
+            SQL Server 格式的表名
+
+        Examples:
+            >>> TableNameConverter.to_sqlserver('dbo_BIPUsers')
+            '[dbo].[BIPUsers]'
+            >>> TableNameConverter.to_sqlserver('productionContractData_26年压力表合同数据')
+            '[productionContractData].[26年压力表合同数据]'
+        """
+        # 分割第一个下划线
+        parts = table_name.split('_', 1)
+        if len(parts) == 2:
+            schema = parts[0]
+            table = parts[1]
+            return f"[{schema}].[{table}]"
+
+        # 如果没有下划线，使用默认 schema dbo
+        return f"[dbo].[{table_name}]"
+
+    @staticmethod
+    def convert_sql(sql: str, db_type: str) -> str:
+        """
+        批量转换 SQL 语句中的表名
+
+        Args:
+            sql: SQL 语句
+            db_type: 目标数据库类型 ('sqlserver' 或 'mysql')
+
+        Returns:
+            转换后的 SQL 语句
+
+        Examples:
+            >>> sql = "SELECT * FROM [dbo].[BIPUsers] WHERE ID = ?"
+            >>> TableNameConverter.convert_sql(sql, 'mysql')
+            'SELECT * FROM dbo_BIPUsers WHERE ID = ?'
+        """
+        if db_type == 'mysql':
+            # SQL Server → MySQL
+            def replace_to_mysql(match):
+                schema = match.group(1)
+                table = match.group(2)
+                return f"{schema}_{table}"
+            result = TableNameConverter.SQLSERVER_PATTERN.sub(replace_to_mysql, sql)
+            return result
+        elif db_type == 'sqlserver':
+            # MySQL → SQL Server
+            # 首先查找可能的 MySQL 格式表名（schema_table 格式）
+            # 这是一个简化版本，可能无法处理所有边缘情况
+            result = sql
+            # 查找单词字符_单词字符 的模式（可能是表名）
+            mysql_pattern = re.compile(r'\b([a-zA-Z_][a-zA-Z0-9_]*)_([a-zA-Z0-9_\u4e00-\u9fff]+)\b')
+            matches = mysql_pattern.findall(result)
+            for schema, table in set(matches):
+                mysql_name = f"{schema}_{table}"
+                sqlserver_name = f"[{schema}].[{table}]"
+                result = result.replace(mysql_name, sqlserver_name)
+            return result
+        return sql
+
+    @staticmethod
+    def extract_table_names(sql: str) -> List[str]:
+        """
+        从 SQL 语句中提取所有表名
+
+        Args:
+            sql: SQL 语句
+
+        Returns:
+            表名列表
+        """
+        tables = []
+        # 查找 SQL Server 格式
+        sqlserver_matches = TableNameConverter.SQLSERVER_PATTERN.findall(sql)
+        for schema, table in sqlserver_matches:
+            tables.append(f"{schema}_{table}")
+
+        # 查找可能的 MySQL 格式
+        mysql_pattern = re.compile(r'\b[a-zA-Z_][a-zA-Z0-9_]*_[a-zA-Z0-9_]+\b')
+        mysql_matches = mysql_pattern.findall(sql)
+        tables.extend(mysql_matches)
+
+        return list(set(tables))