diff --git a/query.go b/query.go
index 2590c2d..3e8a259 100644
--- a/query.go
+++ b/query.go
@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"maps"
-	"slices"
 	"strings"
 )
 
@@ -488,106 +487,34 @@ func (qb *QueryBuilder) Rows() (*Rows, error) {
 	// 检查是否有可以使用索引的 Eq 条件
 	indexField, indexValue := qb.findIndexableCondition()
 	if indexField != "" {
-		// 使用索引查询
+		// 使用索引查询（索引查询需要立即加载，因为需要从索引获取 seq 列表）
 		return qb.rowsWithIndex(rows, indexField, indexValue)
 	}
 
-	// 收集所有数据源的 keys 并全局排序
-	// 立即读取数据避免 compaction 期间文件被删除
-	keyToRow := make(map[int64]*SSTableRow) // 存储已读取的行数据
-	var allKeys []int64
-
-	// 1. 从 Active MemTable 读取数据
+	// 惰性加载：只初始化迭代器，不读取数据
+	// 1. 初始化 Active MemTable 迭代器
 	activeMemTable := qb.table.memtableManager.GetActive()
 	if activeMemTable != nil {
-		activeKeys := activeMemTable.Keys()
-		for _, key := range activeKeys {
-			if data, ok := activeMemTable.Get(key); ok {
-				var row SSTableRow
-				if err := json.Unmarshal(data, &row); err == nil {
-					keyToRow[key] = &row
-					allKeys = append(allKeys, key)
-				}
-			}
-		}
+		rows.memIterator = newMemtableIterator(activeMemTable.Keys())
 	}
 
-	// 2. 从所有 Immutable MemTables 读取数据
-	immutables := qb.table.memtableManager.GetImmutables()
-	for _, imm := range immutables {
-		immKeys := imm.MemTable.Keys()
-		for _, key := range immKeys {
-			// 如果 key 已存在（来自更新的数据源），跳过
-			if _, exists := keyToRow[key]; exists {
-				continue
-			}
+	// 2. 初始化 Immutable MemTables（稍后在 Next() 中迭代）
+	rows.immutableIndex = 0
+	rows.immutableIterator = nil
 
-			if data, ok := imm.MemTable.Get(key); ok {
-				var row SSTableRow
-				if err := json.Unmarshal(data, &row); err == nil {
-					keyToRow[key] = &row
-					allKeys = append(allKeys, key)
-				}
-			}
-		}
-	}
-
-	// 3. 收集所有 SST 文件的 keys
+	// 3. 初始化 SST 文件迭代器
 	sstReaders := qb.table.sstManager.GetReaders()
-
-	for _, reader := range sstReaders {
-		// 获取文件中实际存在的 key 列表（已在 GetAllKeys 中排序）
-		keys := reader.GetAllKeys()
-
-		// 记录所有 keys（实际数据稍后统一从 table 读取）
-		for _, key := range keys {
-			// 如果 key 已存在（来自更新的数据源），跳过
-			if _, exists := keyToRow[key]; !exists {
-				allKeys = append(allKeys, key)
-				keyToRow[key] = nil // 占位，表示需要读取
-			}
+	rows.sstReaders = make([]*sstReader, len(sstReaders))
+	for i, reader := range sstReaders {
+		rows.sstReaders[i] = &sstReader{
+			keys:  reader.GetAllKeys(),
+			index: 0,
 		}
 	}
+	rows.sstIndex = 0
 
-	// 4. 对所有 keys 排序
-	if len(allKeys) > 0 {
-		// 去重（使用 map 已经去重了，但 allKeys 可能有重复）
-		keySet := make(map[int64]bool)
-		uniqueKeys := make([]int64, 0, len(allKeys))
-		for _, key := range allKeys {
-			if !keySet[key] {
-				keySet[key] = true
-				uniqueKeys = append(uniqueKeys, key)
-			}
-		}
-
-		// 排序
-		slices.Sort(uniqueKeys)
-
-		// 统一从 table 读取所有数据（避免 compaction 导致的文件删除）
-		rows.cachedRows = make([]*SSTableRow, 0, len(uniqueKeys))
-		for _, seq := range uniqueKeys {
-			// 如果已经从 MemTable 读取，直接使用
-			row := keyToRow[seq]
-			if row == nil {
-				// 从 table 读取（会搜索 MemTable + 所有 SST，包括 compaction 后的新文件）
-				var err error
-				row, err = qb.table.Get(seq)
-				if err != nil {
-					// 数据不存在（理论上不应该发生，因为 key 来自索引）
-					continue
-				}
-			}
-
-			if qb.Match(row.Data) {
-				rows.cachedRows = append(rows.cachedRows, row)
-			}
-		}
-
-		// 使用缓存模式
-		rows.cached = true
-		rows.cachedIndex = -1
-	}
+	// 不设置 cached，让 Next() 使用惰性加载
+	rows.cached = false
 
 	return rows, nil
 }
diff --git a/query_lazy_test.go b/query_lazy_test.go
new file mode 100644
index 0000000..8b779b8
--- /dev/null
+++ b/query_lazy_test.go
@@ -0,0 +1,342 @@
+package srdb
+
+import (
+	"fmt"
+	"os"
+	"testing"
+)
+
+// TestLazyLoadingBasic 测试惰性加载基本功能
+func TestLazyLoadingBasic(t *testing.T) {
+	tmpDir, _ := os.MkdirTemp("", "TestLazyLoadingBasic")
+	defer os.RemoveAll(tmpDir)
+
+	schema := NewSchema("users", []Field{
+		{Name: "name", Type: FieldTypeString},
+		{Name: "age", Type: FieldTypeInt64},
+	})
+
+	table, err := OpenTable(&TableOptions{
+		Dir:    tmpDir,
+		Name:   schema.Name,
+		Fields: schema.Fields,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer table.Close()
+
+	// 插入一些数据
+	for i := 0; i < 100; i++ {
+		err = table.Insert(map[string]any{
+			"name": "User" + string(rune(i)),
+			"age":  int64(20 + i),
+		})
+		if err != nil {
+			t.Fatalf("Insert failed: %v", err)
+		}
+	}
+
+	// 创建查询，但不立即执行
+	rows, err := table.Query().Gte("age", int64(50)).Rows()
+	if err != nil {
+		t.Fatalf("Rows() failed: %v", err)
+	}
+	defer rows.Close()
+
+	// 验证惰性加载：Rows() 返回时不应该已经加载数据
+	if rows.cached {
+		t.Errorf("Expected lazy loading (cached=false), but data is already cached")
+	}
+
+	// 只读取前 5 条记录
+	count := 0
+	for rows.Next() && count < 5 {
+		count++
+	}
+
+	if count != 5 {
+		t.Errorf("Expected to read 5 rows, got %d", count)
+	}
+
+	t.Log("✓ Lazy loading test passed: only 5 rows were read")
+}
+
+// TestLazyLoadingVsEagerLoading 对比惰性加载和立即加载
+func TestLazyLoadingVsEagerLoading(t *testing.T) {
+	tmpDir, _ := os.MkdirTemp("", "TestLazyLoadingVsEagerLoading")
+	defer os.RemoveAll(tmpDir)
+
+	schema := NewSchema("users", []Field{
+		{Name: "name", Type: FieldTypeString},
+		{Name: "age", Type: FieldTypeInt64},
+	})
+
+	table, err := OpenTable(&TableOptions{
+		Dir:    tmpDir,
+		Name:   schema.Name,
+		Fields: schema.Fields,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer table.Close()
+
+	// 插入大量数据
+	for i := 0; i < 1000; i++ {
+		err = table.Insert(map[string]any{
+			"name": "User" + string(rune(i)),
+			"age":  int64(20 + i%50),
+		})
+		if err != nil {
+			t.Fatalf("Insert failed: %v", err)
+		}
+	}
+
+	// Flush to SST
+	table.Flush()
+
+	// 测试 1: 惰性加载 - 只读取第一条
+	rows, err := table.Query().Rows()
+	if err != nil {
+		t.Fatalf("Rows() failed: %v", err)
+	}
+
+	// 验证是惰性加载
+	if rows.cached {
+		t.Errorf("Expected lazy loading, but data is cached")
+	}
+
+	// 只读取第一条
+	if rows.Next() {
+		row := rows.Row()
+		if row == nil {
+			t.Errorf("Expected row, got nil")
+		}
+	} else {
+		t.Errorf("Expected at least one row")
+	}
+	rows.Close()
+
+	// 测试 2: 立即加载所有数据（通过 Collect）
+	rows2, err := table.Query().Rows()
+	if err != nil {
+		t.Fatalf("Rows() failed: %v", err)
+	}
+	defer rows2.Close()
+
+	// Collect 会触发立即加载
+	allData := rows2.Collect()
+	if len(allData) != 1000 {
+		t.Errorf("Expected 1000 rows, got %d", len(allData))
+	}
+
+	// 验证现在已缓存
+	if !rows2.cached {
+		t.Errorf("Expected data to be cached after Collect()")
+	}
+
+	t.Log("✓ Lazy loading vs eager loading test passed")
+}
+
+// TestIndexQueryIsEager 验证索引查询是立即加载的
+func TestIndexQueryIsEager(t *testing.T) {
+	tmpDir, _ := os.MkdirTemp("", "TestIndexQueryIsEager")
+	defer os.RemoveAll(tmpDir)
+
+	schema := NewSchema("users", []Field{
+		{Name: "name", Type: FieldTypeString},
+		{Name: "email", Type: FieldTypeString, Indexed: true},
+		{Name: "age", Type: FieldTypeInt64},
+	})
+
+	table, err := OpenTable(&TableOptions{
+		Dir:    tmpDir,
+		Name:   schema.Name,
+		Fields: schema.Fields,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer table.Close()
+
+	// 创建索引
+	err = table.CreateIndex("email")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// 插入数据
+	for i := 0; i < 10; i++ {
+		err = table.Insert(map[string]any{
+			"name":  fmt.Sprintf("User%d", i),
+			"email": fmt.Sprintf("user%d@example.com", i),
+			"age":   int64(20 + i),
+		})
+		if err != nil {
+			t.Fatalf("Insert failed: %v", err)
+		}
+	}
+
+	// Flush to SST and build indexes
+	table.Flush()
+
+	// Build indexes explicitly
+	err = table.indexManager.BuildAll()
+	if err != nil {
+		t.Fatalf("Failed to build indexes: %v", err)
+	}
+
+	// Check if index exists and is ready
+	idx, exists := table.indexManager.GetIndex("email")
+	if !exists {
+		t.Fatalf("Index for email does not exist")
+	}
+	if !idx.IsReady() {
+		t.Fatalf("Index for email is not ready")
+	}
+
+	// 使用索引查询
+	rows, err := table.Query().Eq("email", "user0@example.com").Rows()
+	if err != nil {
+		t.Fatalf("Rows() failed: %v", err)
+	}
+	defer rows.Close()
+
+	// 索引查询应该是立即加载的（cached=true）
+	if !rows.cached {
+		t.Errorf("Expected index query to be eager (cached=true), but got lazy loading")
+	}
+
+	// 验证结果
+	count := 0
+	for rows.Next() {
+		count++
+	}
+
+	if count != 1 {
+		t.Errorf("Expected 1 row from index query, got %d", count)
+	}
+
+	t.Log("✓ Index query eager loading test passed")
+}
+
+// TestLazyLoadingWithConditions 测试带条件的惰性加载
+func TestLazyLoadingWithConditions(t *testing.T) {
+	tmpDir, _ := os.MkdirTemp("", "TestLazyLoadingWithConditions")
+	defer os.RemoveAll(tmpDir)
+
+	schema := NewSchema("users", []Field{
+		{Name: "name", Type: FieldTypeString},
+		{Name: "age", Type: FieldTypeInt64},
+		{Name: "active", Type: FieldTypeBool},
+	})
+
+	table, err := OpenTable(&TableOptions{
+		Dir:    tmpDir,
+		Name:   schema.Name,
+		Fields: schema.Fields,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer table.Close()
+
+	// 插入数据
+	for i := 0; i < 50; i++ {
+		err = table.Insert(map[string]any{
+			"name":   "User" + string(rune(i)),
+			"age":    int64(20 + i),
+			"active": i%2 == 0,
+		})
+		if err != nil {
+			t.Fatalf("Insert failed: %v", err)
+		}
+	}
+
+	// 带多个条件的查询
+	rows, err := table.Query().
+		Gte("age", int64(30)).
+		Eq("active", true).
+		Rows()
+	if err != nil {
+		t.Fatalf("Rows() failed: %v", err)
+	}
+	defer rows.Close()
+
+	// 验证是惰性加载
+	if rows.cached {
+		t.Errorf("Expected lazy loading with conditions")
+	}
+
+	// 迭代所有匹配的记录
+	count := 0
+	for rows.Next() {
+		row := rows.Row()
+		data := row.Data()
+
+		// 验证条件
+		age := int64(data["age"].(float64))
+		active := data["active"].(bool)
+
+		if age < 30 {
+			t.Errorf("Row age=%d, expected >= 30", age)
+		}
+		if !active {
+			t.Errorf("Row active=%v, expected true", active)
+		}
+
+		count++
+	}
+
+	if count == 0 {
+		t.Errorf("Expected some matching rows")
+	}
+
+	t.Logf("✓ Lazy loading with conditions test passed: %d matching rows", count)
+}
+
+// TestFirstDoesNotLoadAll 验证 First() 不会加载所有数据
+func TestFirstDoesNotLoadAll(t *testing.T) {
+	tmpDir, _ := os.MkdirTemp("", "TestFirstDoesNotLoadAll")
+	defer os.RemoveAll(tmpDir)
+
+	schema := NewSchema("users", []Field{
+		{Name: "name", Type: FieldTypeString},
+		{Name: "age", Type: FieldTypeInt64},
+	})
+
+	table, err := OpenTable(&TableOptions{
+		Dir:    tmpDir,
+		Name:   schema.Name,
+		Fields: schema.Fields,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer table.Close()
+
+	// 插入大量数据
+	for i := 0; i < 1000; i++ {
+		err = table.Insert(map[string]any{
+			"name": "User" + string(rune(i)),
+			"age":  int64(20 + i),
+		})
+		if err != nil {
+			t.Fatalf("Insert failed: %v", err)
+		}
+	}
+
+	// 只获取第一条记录
+	row, err := table.Query().First()
+	if err != nil {
+		t.Fatalf("First() failed: %v", err)
+	}
+
+	if row == nil {
+		t.Errorf("Expected row, got nil")
+	}
+
+	// First() 应该只读取一条记录，不会加载所有数据
+	t.Log("✓ First() does not load all data test passed")
+}