feat: SQL 语法支持 BETWEEN AND、DROP TABLE IF EXISTS

src/query/ast.ts

@@ -103,6 +103,8 @@ export interface CreateTableStatement {
 export interface DropTableStatement {
   type: 'DROP_TABLE';
   name: string;
+  /** IF EXISTS — 表不存在时不报错 */
+  ifExists?: boolean;
 }
 
 // ---------------------------------------------------------------------------

src/query/executor.ts

@@ -234,6 +234,10 @@ export class QueryExecutor {
   }
 
   private async executeDropTable(stmt: DropTableStatement): Promise<void> {
+    if (stmt.ifExists) {
+      const exists = await this.engine.hasTable(stmt.name);
+      if (!exists) return; // IF EXISTS: 表不存在时静默返回
+    }
     return this.engine.dropTable(stmt.name);
   }
 

src/sql/parser.ts

@@ -423,8 +423,15 @@ export class Parser {
   private parseDropTable(): DropTableStatement {
     this.expect(TokenType.DROP);
     this.expect(TokenType.TABLE);
+    // IF EXISTS（可选）
+    let ifExists = false;
+    if (this.curTokenIs(TokenType.IF)) {
+      this.nextToken();
+      this.expect(TokenType.EXISTS);
+      ifExists = true;
+    }
     const tableName = this.expectIdentifier('table name');
-    return { type: 'DROP_TABLE', name: tableName };
+    return { type: 'DROP_TABLE', name: tableName, ifExists: ifExists || undefined };
   }
 
   // ===================================================================
@@ -483,6 +490,29 @@ export class Parser {
       return result;
     }
 
+    // BETWEEN val1 AND val2
+    if (this.curTokenIs(TokenType.BETWEEN)) {
+      this.nextToken();
+      const low = this.parseValue();
+      this.expect(TokenType.AND);
+      const high = this.parseValue();
+      const result: WhereCondition = {};
+      result[column] = { $gte: low, $lte: high };
+      return result;
+    }
+
+    // NOT BETWEEN val1 AND val2
+    if (this.curTokenIs(TokenType.NOT) && this.peekTokenIs(TokenType.BETWEEN)) {
+      this.nextToken(); // skip NOT
+      this.nextToken(); // skip BETWEEN
+      const low = this.parseValue();
+      this.expect(TokenType.AND);
+      const high = this.parseValue();
+      const result: WhereCondition = {};
+      result[column] = { $not: { $gte: low, $lte: high } };
+      return result;
+    }
+
     // NOT LIKE / NOT IN（NOT 后紧跟 LIKE 或 IN）
     if (this.curTokenIs(TokenType.NOT)) {
       if (this.peekTokenIs(TokenType.IN)) {

src/sql/tokens.ts

@@ -40,6 +40,9 @@ export enum TokenType {
   TRUE = 'TRUE',
   REFERENCES = 'REFERENCES',
   CASCADE = 'CASCADE',
+  BETWEEN = 'BETWEEN',
+  IF = 'IF',
+  EXISTS = 'EXISTS',
   FALSE = 'FALSE',
 
   // JOIN 相关
@@ -133,6 +136,9 @@ export const KEYWORDS: Record<string, TokenType> = {
   'FALSE': TokenType.FALSE,
   'REFERENCES': TokenType.REFERENCES,
   'CASCADE': TokenType.CASCADE,
+  'BETWEEN': TokenType.BETWEEN,
+  'IF': TokenType.IF,
+  'EXISTS': TokenType.EXISTS,
 
   // JOIN
   'INNER': TokenType.INNER,