feat: 新增 DuckDB 方言支持及 SQLite3 自动注册 IF 函数

- 新增 dialect/duckdb 方言，支持 DuckDB SQL 语法
- 新增 schema/dialect/duckdb DDL 操作支持
- dialect/sqlite3: 注册 sqlite3_with_if 驱动，连接时自动注册 IF() 函数
- engine: MakeConnection 对 sqlite3 自动使用带 IF 支持的驱动
- engine: 新增 DBConfig DuckDB 配置项及相关 Option 函数
- 统一各方言测试引用路径

engine/engine_config.go

@@ -68,6 +68,14 @@ type DBConfig struct {
 		KeepAlive         int
 		Dsn               string
 	}
+
+	DuckDB struct {
+		File       string
+		AccessMode string
+		Threads    int
+		MaxMemory  string
+		Dsn        string
+	}
 }
 
 // Option 配置选项类型
@@ -84,6 +92,8 @@ func (c *DBConfig) ToDSN() string {
 		return c.toSQLiteDSN()
 	case "sqlserver":
 		return c.toSQLServerDSN()
+	case "duckdb":
+		return c.toDuckDBDSN()
 	default:
 		panic(fmt.Sprintf("Unsupported driver for DSN generation: %s", c.Driver))
 	}
@@ -279,6 +289,32 @@ func (c *DBConfig) toSQLServerDSN() string {
 	return "sqlserver://" + c.Username + ":" + url.QueryEscape(c.Password) + "@" + host + ":" + c.Port + "?" + params.Encode()
 }
 
+// toDuckDBDSN 生成 DuckDB DSN
+func (c *DBConfig) toDuckDBDSN() string {
+	if c.DuckDB.Dsn != "" {
+		return c.DuckDB.Dsn
+	}
+	// DuckDB 可以使用内存数据库或文件数据库
+	dsn := c.DuckDB.File
+	if dsn == "" {
+		dsn = "" // 空字符串表示内存数据库
+	}
+	params := url.Values{}
+	if c.DuckDB.AccessMode != "" {
+		params.Add("access_mode", c.DuckDB.AccessMode)
+	}
+	if c.DuckDB.Threads > 0 {
+		params.Add("threads", fmt.Sprintf("%d", c.DuckDB.Threads))
+	}
+	if c.DuckDB.MaxMemory != "" {
+		params.Add("max_memory", c.DuckDB.MaxMemory)
+	}
+	if len(params) > 0 {
+		dsn += "?" + params.Encode()
+	}
+	return dsn
+}
+
 // NewDBConfig 创建新的 DBConfig 实例，检查关键参数
 func NewDBConfig(driver string, options ...Option) DBConfig {
 	if driver == "" {
@@ -291,6 +327,7 @@ func NewDBConfig(driver string, options ...Option) DBConfig {
 		"pgsql":     true,
 		"sqlite3":   true,
 		"sqlserver": true,
+		"duckdb":    true,
 	}
 	if !validDrivers[driver] {
 		panic(fmt.Sprintf("Unsupported driver: %s", driver))
@@ -330,6 +367,8 @@ func NewDBConfig(driver string, options ...Option) DBConfig {
 		if config.SQLite.File == "" {
 			panic("File is required for sqlite3 driver")
 		}
+	case "duckdb":
+		// DuckDB 文件参数可选，空字符串表示内存数据库
 	}
 
 	return *config
@@ -447,3 +486,40 @@ func WithSQLServerInstance(instance string) Option {
 		c.SQLServer.Instance = instance
 	}
 }
+
+// DuckDB 专用选项
+func WithDuckDBFile(file string) Option {
+	return func(c *DBConfig) {
+		if c.Driver != "duckdb" {
+			panic("WithDuckDBFile is only valid for duckdb driver")
+		}
+		c.DuckDB.File = file
+	}
+}
+
+func WithDuckDBAccessMode(accessMode string) Option {
+	return func(c *DBConfig) {
+		if c.Driver != "duckdb" {
+			panic("WithDuckDBAccessMode is only valid for duckdb driver")
+		}
+		c.DuckDB.AccessMode = accessMode
+	}
+}
+
+func WithDuckDBThreads(threads int) Option {
+	return func(c *DBConfig) {
+		if c.Driver != "duckdb" {
+			panic("WithDuckDBThreads is only valid for duckdb driver")
+		}
+		c.DuckDB.Threads = threads
+	}
+}
+
+func WithDuckDBMaxMemory(maxMemory string) Option {
+	return func(c *DBConfig) {
+		if c.Driver != "duckdb" {
+			panic("WithDuckDBMaxMemory is only valid for duckdb driver")
+		}
+		c.DuckDB.MaxMemory = maxMemory
+	}
+}