release: v0.4.1 — Aria 级联/ALTER/clearAll + 流式查询/派生表 + 正确性加固

新增：
- AriaEngine 外键级联（CASCADE/SET NULL/RESTRICT）+ clearAll() 重置 API
- 引擎级 alterTable：Aria DROP COLUMN 重写存储行 + schema 持久化
- 流式查询 queryStream / findStream（LSM 惰性扫描不物化）
- FROM 派生表 / 多列 ON 哈希连接 / COUNT(DISTINCT) / NULLS FIRST/LAST
- 普通列别名 + ORDER BY 别名 + 无表查询 + 字符串常量列
- 演示页引擎切换器（Memory/Aria）+ 预设自动重置

修复：
- Aria WAL DROP_TABLE 崩溃恢复（删表复活）+ 恢复后 WAL 截断
- Memory update/delete 索引维护（unique 约束绕过）
- 关联 EXISTS 绑定失效 / HAVING 标量子查询 / INSERT SELECT 位置错位
- 裸布尔列条件（WHERE done / CASE WHEN done）
- Aria $in 重复行 / JOIN 主表 WHERE 下推 / DROP INDEX 报错
- ORDER BY/GROUP BY/SELECT 表前缀列 + SQL '' 标准转义

质量：894 测试 · 47 套件 · 81.5% 覆盖率

src/engine/memory.ts

@@ -97,6 +97,29 @@ export class MemoryEngine implements IStorageEngine {
     return results;
   }
 
+  /** v0.4.0: 流式查询 — 逐行回调（单次迭代，不物化结果数组） */
+  async findStream(tableName: string, query: QueryPlan, onRow: (row: Record<string, unknown>) => void): Promise<number> {
+    this.ensureTable(tableName);
+    const table = this.tables.get(tableName)!;
+    const hasWhere = !!(query.where && Object.keys(query.where).length > 0);
+    const limit = query.limit ?? Infinity;
+    const offset = query.offset ?? 0;
+    const project = query.columns && query.columns.length > 0 && query.columns[0] !== '*'
+      ? (row: Record<string, unknown>) => projectColumns(row, query.columns!)
+      : null;
+
+    let count = 0;
+    let skipped = 0;
+    for (const row of table.values()) {
+      if (hasWhere && !matchWhere(row, query.where!)) continue;
+      if (skipped < offset) { skipped++; continue; }
+      onRow(project ? project(row) : row);
+      count++;
+      if (count >= limit) break;
+    }
+    return count;
+  }
+
   async update(tableName: string, query: QueryPlan, updates: Record<string, unknown>): Promise<number> {
     this.ensureTable(tableName);
     const schema = this.schemas.get(tableName)!;
@@ -104,9 +127,13 @@ export class MemoryEngine implements IStorageEngine {
     let count = 0;
     for (const [pk, row] of table) {
       if (!query.where || Object.keys(query.where).length === 0 || matchWhere(row, query.where)) {
+        // v0.3.3: 先移除旧值索引条目（修复 update 后唯一约束被绕过、按新值查索引丢行）
+        this.removeIndexEntries(tableName, row, pk);
         const updated = { ...row, ...updates };
         this.validateRow(schema, updated);
+        this.checkUniqueness(schema, updated);
         table.set(pk, updated);
+        this.updateIndexes(tableName, updated, pk);
         count++;
       }
     }
@@ -119,6 +146,8 @@ export class MemoryEngine implements IStorageEngine {
     const toDelete: string[] = [];
     for (const [pk, row] of table) {
       if (!query.where || Object.keys(query.where).length === 0 || matchWhere(row, query.where)) {
+        // v0.3.3: 删除行前清理其索引条目（修复删除后索引残留）
+        this.removeIndexEntries(tableName, row, pk);
         toDelete.push(pk);
       }
     }
@@ -177,6 +206,10 @@ export class MemoryEngine implements IStorageEngine {
     const schema = this.schemas.get(tableName)!;
     const colDef = schema.columns[column];
     if (!colDef) throw new DatabaseError(`Column "${column}" does not exist in table "${tableName}"`, 'COLUMN_NOT_FOUND');
+    // v0.4.1: DROP 不存在的索引应报错（此前静默成功）
+    if (!colDef.index && !colDef.unique) {
+      throw new DatabaseError(`Index on column "${column}" does not exist in table "${tableName}"`, 'INDEX_NOT_FOUND');
+    }
     colDef.index = false;
     colDef.unique = false;
     const tableIndexes = this.indexes.get(tableName);
@@ -288,17 +321,24 @@ export class MemoryEngine implements IStorageEngine {
     const tableIndexes = this.indexes.get(tableName);
     if (!tableIndexes || !query.where) return Array.from(table.values());
     for (const [col, condition] of Object.entries(query.where)) {
+      // v0.4.1: 支持 { $eq: value } 形式（SQL 解析器生成的等值条件）走索引
+      let targetValue: unknown;
       if (typeof condition !== 'object' || condition === null) {
-        const colIndex = tableIndexes.get(col);
-        if (colIndex) {
-          const pks = colIndex.get(condition);
-          if (pks) {
-            const result: Record<string, unknown>[] = [];
-            for (const pk of pks) { const r = table.get(pk); if (r) result.push(r); }
-            return result;
-          }
-          return [];
+        targetValue = condition;
+      } else if ('$eq' in (condition as Record<string, unknown>) && Object.keys(condition as Record<string, unknown>).length === 1) {
+        targetValue = (condition as Record<string, unknown>).$eq;
+      } else {
+        continue;
+      }
+      const colIndex = tableIndexes.get(col);
+      if (colIndex) {
+        const pks = colIndex.get(targetValue);
+        if (pks) {
+          const result: Record<string, unknown>[] = [];
+          for (const pk of pks) { const r = table.get(pk); if (r) result.push(r); }
+          return result;
         }
+        return [];
       }
     }
     return Array.from(table.values());
@@ -317,6 +357,22 @@ export class MemoryEngine implements IStorageEngine {
     }
   }
 
+  /** v0.3.3: 从所有索引中移除一行的条目（update/delete 前调用，修复索引过期/残留） */
+  private removeIndexEntries(tableName: string, row: Record<string, unknown>, pk: string): void {
+    const tableIndexes = this.indexes.get(tableName);
+    if (!tableIndexes) return;
+    for (const [colName, colIndex] of tableIndexes) {
+      const value = row[colName];
+      if (value !== undefined && value !== null) {
+        const pks = colIndex.get(value);
+        if (pks) {
+          pks.delete(pk);
+          if (pks.size === 0) colIndex.delete(value);
+        }
+      }
+    }
+  }
+
   // ---- 外键级联 ----
 
   /**
@@ -359,6 +415,8 @@ export class MemoryEngine implements IStorageEngine {
           for (const refPk of toDelete) {
             const refRow = refTableData.get(refPk);
             if (refRow) {
+              // v0.3.3: 级联删除前清理索引条目
+              this.removeIndexEntries(refTableName, refRow, refPk);
               totalCascade += await this.cascadeDelete(refTableName, refPk, refRow);
             }
             refTableData.delete(refPk);
@@ -368,6 +426,13 @@ export class MemoryEngine implements IStorageEngine {
           for (const refPk of toDelete) {
             const refRow = refTableData.get(refPk);
             if (refRow) {
+              // v0.3.3: 外键列置空后同步更新索引
+              if (refRow[colName] !== undefined && refRow[colName] !== null) {
+                const pks = this.indexes.get(refTableName)?.get(colName);
+                if (pks) {
+                  pks.get(refRow[colName])?.delete(refPk);
+                }
+              }
               refRow[colName] = null;
             }
           }