最新的GRDB中有一个trace函数：

// Prints all SQL statements
var config = Configuration()
config.prepareDatabase { db in
    db.trace { print($0) }
}

如何将请求打印为SQL？常见问题解答指出：
您可以将请求转换为SQLRequest示例：

try dbQueue.read { db in
    let request = Wine
        .filter(Column("origin") == "Burgundy")
        .order(Column("price")

    let sqlRequest = try SQLRequest(db, request: request)
    print(sqlRequest.sql)
    // Prints SELECT * FROM wine WHERE origin = ? ORDER BY price
    print(sqlRequest.arguments)
    // Prints ["Burgundy"]
}

对于较新版本的GRDB，答案是不同的。
摘自如何将请求打印为SQL？：

try dbQueue.read { db in
    let request = Player.filter(Column("email") == "arthur@example.com")
    let statement = try request.makePreparedRequest(db).statement
    print(statement) // SELECT * FROM player WHERE email = ?
    print(statement.arguments) // ["arthur@example.com"]
}