diff --git a/adapter/sqlite3/sqlite3.go b/adapter/sqlite3/sqlite3.go
deleted file mode 100644
index 73d3232b..00000000
--- a/adapter/sqlite3/sqlite3.go
+++ /dev/null
@@ -1,127 +0,0 @@
-// Package sqlite3 wraps go-sqlite3 driver as an adapter for rel.
-//
-// Deprecated: Please use github.com/go-rel/sqlite3 instead.
-//
-// Usage:
-//	// open sqlite3 connection.
-//	adapter, err := sqlite3.Open("dev.db")
-//	if err != nil {
-//		panic(err)
-//	}
-//	defer adapter.Close()
-//
-//	// initialize rel's repo.
-//	repo := rel.New(adapter)
-package sqlite3
-
-import (
-	db "database/sql"
-	"strings"
-
-	"github.com/go-rel/rel"
-	"github.com/go-rel/rel/adapter/sql"
-)
-
-// Adapter definition for mysql database.
-type Adapter struct {
-	*sql.Adapter
-}
-
-var (
-	_ rel.Adapter = (*Adapter)(nil)
-
-	// Config for mysql adapter.
-	Config = sql.Config{
-		Placeholder:         "?",
-		EscapeChar:          "`",
-		InsertDefaultValues: true,
-		IncrementFunc:       incrementFunc,
-		ErrorFunc:           errorFunc,
-		MapColumnFunc:       mapColumnFunc,
-	}
-)
-
-// New sqlite adapter using existing connection.
-//
-// Deprecated: Please use github.com/go-rel/sqlite3 instead.
-func New(database *db.DB) *Adapter {
-	return &Adapter{
-		Adapter: &sql.Adapter{
-			Config: Config,
-			DB:     database,
-		},
-	}
-}
-
-// Open sqlite connection using dsn.
-func Open(dsn string) (*Adapter, error) {
-	var database, err = db.Open("sqlite3", dsn)
-	return New(database), err
-}
-
-func incrementFunc(adapter sql.Adapter) int {
-	// decrement
-	return -1
-}
-
-func errorFunc(err error) error {
-	if err == nil {
-		return nil
-	}
-
-	var (
-		msg         = err.Error()
-		failedSep   = " failed: "
-		failedIndex = strings.Index(msg, failedSep)
-		failedLen   = 9 // len(failedSep)
-	)
-
-	if failedIndex < 0 {
-		failedIndex = 0
-	}
-
-	switch msg[:failedIndex] {
-	case "UNIQUE constraint":
-		return rel.ConstraintError{
-			Key:  msg[failedIndex+failedLen:],
-			Type: rel.UniqueConstraint,
-			Err:  err,
-		}
-	case "CHECK constraint":
-		return rel.ConstraintError{
-			Key:  msg[failedIndex+failedLen:],
-			Type: rel.CheckConstraint,
-			Err:  err,
-		}
-	default:
-		return err
-	}
-}
-
-func mapColumnFunc(column *rel.Column) (string, int, int) {
-	var (
-		typ      string
-		m, n     int
-		unsigned = column.Unsigned
-	)
-
-	column.Unsigned = false
-
-	switch column.Type {
-	case rel.ID:
-		typ = "INTEGER PRIMARY KEY"
-	case rel.BigID:
-		typ = "BIGINT PRIMARY KEY"
-	case rel.Int:
-		typ = "INTEGER"
-		m = column.Limit
-	default:
-		typ, m, n = sql.MapColumn(column)
-	}
-
-	if unsigned {
-		typ = "UNSIGNED " + typ
-	}
-
-	return typ, m, n
-}
diff --git a/adapter/sqlite3/sqlite3_test.go b/adapter/sqlite3/sqlite3_test.go
deleted file mode 100644
index e3f0793e..00000000
--- a/adapter/sqlite3/sqlite3_test.go
+++ /dev/null
@@ -1,120 +0,0 @@
-package sqlite3
-
-import (
-	"context"
-	"os"
-	"testing"
-
-	"github.com/go-rel/rel"
-	"github.com/go-rel/rel/adapter/specs"
-	_ "github.com/mattn/go-sqlite3"
-	"github.com/stretchr/testify/assert"
-)
-
-var ctx = context.TODO()
-
-func dsn() string {
-	if os.Getenv("SQLITE3_DATABASE") != "" {
-		return os.Getenv("SQLITE3_DATABASE") + "?_foreign_keys=1&_loc=Local"
-	}
-
-	return "./rel_test.db?_foreign_keys=1&_loc=Local"
-}
-
-func TestAdapter_specs(t *testing.T) {
-	adapter, err := Open(dsn())
-	assert.Nil(t, err)
-	defer adapter.Close()
-
-	repo := rel.New(adapter)
-
-	// Prepare tables
-	teardown := specs.Setup(t, repo)
-	defer teardown()
-
-	// Migration Specs
-	specs.Migrate(t, repo, specs.SkipDropColumn)
-
-	// Query Specs
-	specs.Query(t, repo)
-	specs.QueryJoin(t, repo)
-	specs.QueryWhereSubQuery(t, repo, specs.SkipAllAndAnyKeyword)
-	specs.QueryNotFound(t, repo)
-
-	// Preload specs
-	specs.PreloadHasMany(t, repo)
-	specs.PreloadHasManyWithQuery(t, repo)
-	specs.PreloadHasManySlice(t, repo)
-	specs.PreloadHasOne(t, repo)
-	specs.PreloadHasOneWithQuery(t, repo)
-	specs.PreloadHasOneSlice(t, repo)
-	specs.PreloadBelongsTo(t, repo)
-	specs.PreloadBelongsToWithQuery(t, repo)
-	specs.PreloadBelongsToSlice(t, repo)
-
-	// Aggregate Specs
-	specs.Aggregate(t, repo)
-
-	// Insert Specs
-	specs.Insert(t, repo)
-	specs.InsertHasMany(t, repo)
-	specs.InsertHasOne(t, repo)
-	specs.InsertBelongsTo(t, repo)
-	specs.Inserts(t, repo)
-	specs.InsertAll(t, repo)
-	// specs.InsertAllPartialCustomPrimary(t, repo) - not supported
-
-	// Update Specs
-	specs.Update(t, repo)
-	specs.UpdateNotFound(t, repo)
-	specs.UpdateHasManyInsert(t, repo)
-	specs.UpdateHasManyUpdate(t, repo)
-	specs.UpdateHasManyReplace(t, repo)
-	specs.UpdateHasOneInsert(t, repo)
-	specs.UpdateHasOneUpdate(t, repo)
-	specs.UpdateBelongsToInsert(t, repo)
-	specs.UpdateBelongsToUpdate(t, repo)
-	specs.UpdateAtomic(t, repo)
-	specs.Updates(t, repo)
-	specs.UpdateAny(t, repo)
-
-	// Delete specs
-	specs.Delete(t, repo)
-	specs.DeleteBelongsTo(t, repo)
-	specs.DeleteHasOne(t, repo)
-	specs.DeleteHasMany(t, repo)
-	specs.DeleteAll(t, repo)
-	specs.DeleteAny(t, repo)
-
-	// Constraint specs
-	// - foreign key constraint is not supported because of lack of information in the error message.
-	specs.UniqueConstraintOnInsert(t, repo)
-	specs.UniqueConstraintOnUpdate(t, repo)
-	specs.CheckConstraintOnInsert(t, repo)
-	specs.CheckConstraintOnUpdate(t, repo)
-}
-
-func TestAdapter_Transaction_commitError(t *testing.T) {
-	adapter, err := Open(dsn())
-	assert.Nil(t, err)
-	defer adapter.Close()
-
-	assert.NotNil(t, adapter.Commit(ctx))
-}
-
-func TestAdapter_Transaction_rollbackError(t *testing.T) {
-	adapter, err := Open(dsn())
-	assert.Nil(t, err)
-	defer adapter.Close()
-
-	assert.NotNil(t, adapter.Rollback(ctx))
-}
-
-func TestAdapter_Exec_error(t *testing.T) {
-	adapter, err := Open(dsn())
-	assert.Nil(t, err)
-	defer adapter.Close()
-
-	_, _, err = adapter.Exec(ctx, "error", nil)
-	assert.NotNil(t, err)
-}
diff --git a/cmd/rel/internal/migrate_test.go b/cmd/rel/internal/migrate_test.go
index 353404b0..3136ea84 100644
--- a/cmd/rel/internal/migrate_test.go
+++ b/cmd/rel/internal/migrate_test.go
@@ -29,7 +29,7 @@ func TestExecMigrate(t *testing.T) {
 			args = []string{
 				"rel",
 				"migrate",
-				"-adapter=github.com/go-rel/rel/adapter/sqlite3",
+				"-adapter=github.com/go-rel/sqlite3",
 				"-driver=github.com/mattn/go-sqlite3",
 				"-dsn=:memory:",
 				"-dir=db",
@@ -47,7 +47,7 @@ func TestExecMigrate(t *testing.T) {
 				"migrate",
 				"-dir=testdata/migrations",
 				"-module=github.com/go-rel/rel/cmd/rel/internal",
-				"-adapter=github.com/go-rel/rel/adapter/sqlite3",
+				"-adapter=github.com/go-rel/sqlite3",
 				"-driver=github.com/mattn/go-sqlite3",
 				"-dsn=:memory:",
 				"-verbose=false",
diff --git a/cmd/rel/internal/util.go b/cmd/rel/internal/util.go
index 83abb183..609c8cdd 100644
--- a/cmd/rel/internal/util.go
+++ b/cmd/rel/internal/util.go
@@ -22,11 +22,11 @@ func getDatabaseInfo() (string, string, string) {
 		driver = os.Getenv("DATABASE_DRIVER")
 		dsn = os.Getenv("DATABASE_URL")
 	case os.Getenv("SQLITE3_DATABASE") != "":
-		adapter = "github.com/go-rel/rel/adapter/sqlite3"
+		adapter = "github.com/go-rel/sqlite3"
 		driver = "github.com/mattn/go-sqlite3"
 		dsn = os.Getenv("SQLITE3_DATABASE")
 	case os.Getenv("MYSQL_HOST") != "":
-		adapter = "github.com/go-rel/rel/adapter/mysql"
+		adapter = "github.com/go-rel/mysql"
 		driver = "github.com/go-sql-driver/mysql"
 		dsn = fmt.Sprintf("%s:%s@(%s:%s)/%s?charset=utf8&parseTime=True&loc=Local",
 			os.Getenv("MYSQL_USERNAME"),
@@ -35,7 +35,7 @@ func getDatabaseInfo() (string, string, string) {
 			os.Getenv("MYSQL_PORT"),
 			os.Getenv("MYSQL_DATABASE"))
 	case os.Getenv("POSTGRES_HOST") != "":
-		adapter = "github.com/go-rel/rel/adapter/postgres"
+		adapter = "github.com/go-rel/postgres"
 		driver = "github.com/lib/pq"
 		dsn = fmt.Sprintf("postgres://%s:%s@%s:%s/%s?sslmode=disable",
 			os.Getenv("POSTGRES_USERNAME"),
@@ -44,7 +44,7 @@ func getDatabaseInfo() (string, string, string) {
 			os.Getenv("POSTGRES_PORT"),
 			os.Getenv("POSTGRES_DATABASE"))
 	case os.Getenv("POSTGRESQL_HOST") != "":
-		adapter = "github.com/go-rel/rel/adapter/postgres"
+		adapter = "github.com/go-rel/postgres"
 		driver = "github.com/lib/pq"
 		dsn = fmt.Sprintf("postgres://%s:%s@%s:%s/%s?sslmode=disable",
 			os.Getenv("POSTGRESQL_USERNAME"),
diff --git a/cmd/rel/internal/util_test.go b/cmd/rel/internal/util_test.go
index b8b2313c..150123c7 100644
--- a/cmd/rel/internal/util_test.go
+++ b/cmd/rel/internal/util_test.go
@@ -11,7 +11,7 @@ import (
 
 func TestGetDatabaseInfo(t *testing.T) {
 	t.Run("database", func(t *testing.T) {
-		os.Setenv("DATABASE_ADAPTER", "github.com/go-rel/rel/adapter/mysql")
+		os.Setenv("DATABASE_ADAPTER", "github.com/go-rel/mysql")
 		os.Setenv("DATABASE_DRIVER", "github.com/go-sql-driver/mysql")
 		os.Setenv("DATABASE_URL", "user:password@(localhost:3306)/db?charset=utf8&parseTime=True&loc=Local")
 
@@ -20,7 +20,7 @@ func TestGetDatabaseInfo(t *testing.T) {
 		defer os.Setenv("DATABASE_URL", "")
 
 		adapter, driver, url := getDatabaseInfo()
-		assert.Equal(t, "github.com/go-rel/rel/adapter/mysql", adapter)
+		assert.Equal(t, "github.com/go-rel/mysql", adapter)
 		assert.Equal(t, "github.com/go-sql-driver/mysql", driver)
 		assert.Equal(t, "user:password@(localhost:3306)/db?charset=utf8&parseTime=True&loc=Local", url)
 	})
@@ -39,7 +39,7 @@ func TestGetDatabaseInfo(t *testing.T) {
 		defer os.Setenv("MYSQL_PASSWORD", "")
 
 		adapter, driver, url := getDatabaseInfo()
-		assert.Equal(t, "github.com/go-rel/rel/adapter/mysql", adapter)
+		assert.Equal(t, "github.com/go-rel/mysql", adapter)
 		assert.Equal(t, "github.com/go-sql-driver/mysql", driver)
 		assert.Equal(t, "user:password@(localhost:3306)/db?charset=utf8&parseTime=True&loc=Local", url)
 	})
@@ -58,7 +58,7 @@ func TestGetDatabaseInfo(t *testing.T) {
 		defer os.Setenv("POSTGRES_PASSWORD", "")
 
 		adapter, driver, url := getDatabaseInfo()
-		assert.Equal(t, "github.com/go-rel/rel/adapter/postgres", adapter)
+		assert.Equal(t, "github.com/go-rel/postgres", adapter)
 		assert.Equal(t, "github.com/lib/pq", driver)
 		assert.Equal(t, "postgres://user:password@localhost:5432/db?sslmode=disable", url)
 	})
@@ -77,7 +77,7 @@ func TestGetDatabaseInfo(t *testing.T) {
 		defer os.Setenv("POSTGRESQL_PASSWORD", "")
 
 		adapter, driver, url := getDatabaseInfo()
-		assert.Equal(t, "github.com/go-rel/rel/adapter/postgres", adapter)
+		assert.Equal(t, "github.com/go-rel/postgres", adapter)
 		assert.Equal(t, "github.com/lib/pq", driver)
 		assert.Equal(t, "postgres://user:password@localhost:5432/db?sslmode=disable", url)
 	})
@@ -87,7 +87,7 @@ func TestGetDatabaseInfo(t *testing.T) {
 		defer os.Setenv("SQLITE3_DATABASE", "")
 
 		adapter, driver, url := getDatabaseInfo()
-		assert.Equal(t, "github.com/go-rel/rel/adapter/sqlite3", adapter)
+		assert.Equal(t, "github.com/go-rel/sqlite3", adapter)
 		assert.Equal(t, "github.com/mattn/go-sqlite3", driver)
 		assert.Equal(t, "test.db", url)
 	})