在mysql中使用INDEX和INSERT UNIQUE VALUES插入IGNORE

Question

我有下表：

CREATE TABLE `Triples` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`Subject` longtext COLLATE utf8mb4_unicode_ci,
`Predicate` longtext COLLATE utf8mb4_unicode_ci,
`Object` longtext COLLATE utf8mb4_unicode_ci,
`SubHash` binary(16) DEFAULT NULL,
`PredHash` binary(16) DEFAULT NULL,
`ObHash` binary(16) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `PredHash` (`PredHash`),
KEY `ObHash` (`ObHash`),
KEY `SubHash` (`SubHash`)
) ENGINE=InnoDB

它包含大约8亿行。 现在我想创建另外两个表。 一个表是节点：

CREATE TABLE `Nodes` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`val_hash` binary(16) NOT NULL,
`val` longtext COLLATE utf8mb4_unicode_ci NOT NULL,
`subjectCount` bigint(20) unsigned NOT NULL DEFAULT '0',
`objectCount` bigint(20) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
)

这将一次存储三元组中的所有主题和对象（插入数据后val_hash将成为一个键）。 问题是哪个INSERT表现更好？：

INSERT INTO Nodes(val,val_hash)
SELECT j.val,j.val_hash FROM (SELECT Subject as val, SubHash as val_hash 
FROM Triples GROUP BY val_hash
UNION
SELECT Object as val, ObHash as val_hash 
FROM Triples GROUP BY val_hash) as j
GROUP BY j.val_hash

或以下：

ALTER TABLE Nodes
ADD UNIQUE KEY(val_hash);
INSERT IGNORE INTO Nodes(val,val_hash)
SELECT Subject,SubHash FROM Triples GROUP BY SubHash;
INSERT IGNORE INTO Nodes(val,val_hash)
SELECT Object,ObHash FROM Triples GROUP BY ObHash;    

我问，因为密钥增加了插入的复杂性，但是工会需要一个临时表，我不知道在这种情况下哪一个更好。