diff --git a/ch/db.go b/ch/db.go
index b1bed78..f1f3eef 100644
--- a/ch/db.go
+++ b/ch/db.go
@@ -325,6 +325,7 @@ func (db *DB) _query(ctx context.Context, query string) (*blockIter, error) {
 		db.writeQuery(ctx, cn, wr, query)
 		db.writeBlock(ctx, wr, nil)
 	}); err != nil {
+		db.releaseConn(cn, err)
 		return nil, err
 	}
 
diff --git a/ch/query_select.go b/ch/query_select.go
index d01738e..9364067 100644
--- a/ch/query_select.go
+++ b/ch/query_select.go
@@ -12,11 +12,6 @@ import (
 	"github.com/uptrace/go-clickhouse/ch/internal"
 )
 
-type union struct {
-	expr  string
-	query *SelectQuery
-}
-
 type SelectQuery struct {
 	baseQuery
 
@@ -31,8 +26,12 @@ type SelectQuery struct {
 	limit      int
 	offset     int
 	final      bool
+	union      []union
+}
 
-	union []union
+type union struct {
+	expr  string
+	query *SelectQuery
 }
 
 var _ Query = (*SelectQuery)(nil)
@@ -162,7 +161,7 @@ func (q *SelectQuery) ExcludeColumn(columns ...string) *SelectQuery {
 	return q
 }
 
-///------------------------------------------------------------------------------
+//------------------------------------------------------------------------------
 
 func (q *SelectQuery) Union(other *SelectQuery) *SelectQuery {
 	return q.addUnion(" UNION ", other)
diff --git a/ch/testdata/snapshots/TestQuery-19 b/ch/testdata/snapshots/TestQuery-19
index ca7a15c..ab1d053 100644
--- a/ch/testdata/snapshots/TestQuery-19
+++ b/ch/testdata/snapshots/TestQuery-19
@@ -1 +1 @@
-CREATE TABLE IF NOT EXISTS "my-table_dist" AS "my-table" ON CLUSTER "my-cluster" Engine = Distributed("my-cluster", currentDatabase(), "my-table", rand())
+CREATE TABLE IF NOT EXISTS "my-table_dist" ON CLUSTER "my-cluster" AS "my-table" Engine = Distributed("my-cluster", currentDatabase(), "my-table", rand())