UNION with more than two statements produces an incorrect query according to MySQL/MariaDB

[panta]

Describe the bug
When using UNION on the result of another UNION, the resulting query makes MySQL/MariaDB complain.

Environment (please complete the following information):

• OS: macos
• Database: MariaDB 10.3
• Database driver: go-sql-driver/mysql
• Jet version v2.10.1

Code snippet

	stmt1 := SELECT(Int(1).AS("value"))
	stmt2 := SELECT(Int(2).AS("value"))
	stmt3 := SELECT(Int(3).AS("value"))
	stmt := UNION(stmt1, stmt2)
	stmt = UNION(stmt, stmt3)
	debugSql := stmt.DebugSql()
	log.Printf("SQL: %s", debugSql)

	var res []struct {
		Value int `db:"value" alias:"value"`
	}

	if err := stmt.Query(db, &res); err != nil {
		panic(err)
	}
	log.Printf("results: %#v", res)

Resulting query:

(
     (
          SELECT 1 AS "value"
     )
     UNION
     (
          SELECT 2 AS "value"
     )
)
UNION
(
     SELECT 3 AS "value"
);

Resulting error:

jet: Error 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'UNION\n     (\n          SELECT ? AS \"value\"\n     )\n)\nUNION\n(\n     SELECT ? AS ...' at line 5

Expected behavior
I'd expect a query that doesn't return error, like:

(
     SELECT 1 AS "value"
)
UNION
(
     SELECT 2 AS "value"
)
UNION
(
     SELECT 3 AS "value"
);

[go-jet]

It seems to be an issue with MariaDB 10.3, as it works as expected in MariaDB 11.3.

For the expected query, why not:

stmt1 := SELECT(Int(1).AS("value"))
stmt2 := SELECT(Int(2).AS("value"))
stmt3 := SELECT(Int(3).AS("value"))
stmt := UNION(stmt1, stmt2, stmt3)