diff --git a/internal/db/sql_pool.go b/internal/db/sql_pool.go
index 13620c3f..e8f2608c 100644
--- a/internal/db/sql_pool.go
+++ b/internal/db/sql_pool.go
@@ -8,6 +8,7 @@ import (
 
 const (
 	defaultSQLMaxOpenConns    = 4
+	defaultSQLMaxIdleConns    = 1
 	defaultSQLConnMaxLifetime = 30 * time.Minute
 	defaultSQLConnMaxIdleTime = 30 * time.Second
 )
@@ -21,7 +22,13 @@ func configureSQLConnectionPool(db *sql.DB, dbType string) {
 		return
 	case "oracle", "oceanbase":
 		db.SetMaxOpenConns(defaultSQLMaxOpenConns)
-		db.SetMaxIdleConns(1)
+		db.SetMaxIdleConns(defaultSQLMaxIdleConns)
+		db.SetConnMaxIdleTime(defaultSQLConnMaxIdleTime)
+		db.SetConnMaxLifetime(defaultSQLConnMaxLifetime)
+		return
+	case "sqlserver":
+		db.SetMaxOpenConns(defaultSQLMaxOpenConns)
+		db.SetMaxIdleConns(defaultSQLMaxIdleConns)
 		db.SetConnMaxIdleTime(defaultSQLConnMaxIdleTime)
 		db.SetConnMaxLifetime(defaultSQLConnMaxLifetime)
 		return
diff --git a/internal/db/sql_pool_test.go b/internal/db/sql_pool_test.go
new file mode 100644
index 00000000..45f4c947
--- /dev/null
+++ b/internal/db/sql_pool_test.go
@@ -0,0 +1,102 @@
+package db
+
+import (
+	"context"
+	"database/sql"
+	"database/sql/driver"
+	"errors"
+	"sync/atomic"
+	"testing"
+)
+
+const poolRecordingDriverName = "gonavi_pool_recording"
+
+var (
+	poolRecordingOpenCount  atomic.Int64
+	poolRecordingCloseCount atomic.Int64
+)
+
+func init() {
+	sql.Register(poolRecordingDriverName, poolRecordingDriver{})
+}
+
+type poolRecordingDriver struct{}
+
+func (poolRecordingDriver) Open(name string) (driver.Conn, error) {
+	poolRecordingOpenCount.Add(1)
+	return poolRecordingConn{}, nil
+}
+
+type poolRecordingConn struct{}
+
+func (poolRecordingConn) Prepare(query string) (driver.Stmt, error) {
+	return nil, errors.New("not implemented")
+}
+
+func (poolRecordingConn) Close() error {
+	poolRecordingCloseCount.Add(1)
+	return nil
+}
+
+func (poolRecordingConn) Begin() (driver.Tx, error) {
+	return nil, errors.New("not implemented")
+}
+
+func (poolRecordingConn) Ping(ctx context.Context) error {
+	return nil
+}
+
+func resetPoolRecordingDriverCounters() {
+	poolRecordingOpenCount.Store(0)
+	poolRecordingCloseCount.Store(0)
+}
+
+func openConfiguredPoolForTest(t *testing.T, dbType string) *sql.DB {
+	t.Helper()
+	resetPoolRecordingDriverCounters()
+	dbConn, err := sql.Open(poolRecordingDriverName, t.Name())
+	if err != nil {
+		t.Fatalf("sql.Open failed: %v", err)
+	}
+	configureSQLConnectionPool(dbConn, dbType)
+	t.Cleanup(func() {
+		_ = dbConn.Close()
+	})
+	return dbConn
+}
+
+func TestConfigureSQLConnectionPoolKeepsOneIdleSQLServerConnection(t *testing.T) {
+	dbConn := openConfiguredPoolForTest(t, "sqlserver")
+
+	if err := dbConn.PingContext(context.Background()); err != nil {
+		t.Fatalf("first ping failed: %v", err)
+	}
+	if err := dbConn.PingContext(context.Background()); err != nil {
+		t.Fatalf("second ping failed: %v", err)
+	}
+
+	if got := poolRecordingOpenCount.Load(); got != 1 {
+		t.Fatalf("expected SQL Server pool to reuse one idle connection, opened %d connections", got)
+	}
+	if got := poolRecordingCloseCount.Load(); got != 0 {
+		t.Fatalf("expected SQL Server idle connection to remain cached before DB close, closed %d connections", got)
+	}
+}
+
+func TestConfigureSQLConnectionPoolDefaultDoesNotKeepIdleConnections(t *testing.T) {
+	dbConn := openConfiguredPoolForTest(t, "mysql")
+
+	if err := dbConn.PingContext(context.Background()); err != nil {
+		t.Fatalf("first ping failed: %v", err)
+	}
+	if err := dbConn.PingContext(context.Background()); err != nil {
+		t.Fatalf("second ping failed: %v", err)
+	}
+
+	if got := poolRecordingOpenCount.Load(); got != 2 {
+		t.Fatalf("expected default pool to reopen without idle cache, opened %d connections", got)
+	}
+	if got := poolRecordingCloseCount.Load(); got != 2 {
+		t.Fatalf("expected default pool to close each returned connection, closed %d connections", got)
+	}
+}