SQL优化之用union all取代in或or测试

WHERE * FROM article
WHERE article_category=2
OR article_category=3
ORDER BY article_id DESC
LIMIT 5
// 执行时间：11.0777

SELECT * FROM article
WHERE article_category IN (2,3)
ORDER BY article_id DESC
LIMIT 5
// 执行时间：11.2850

(
    SELECT * FROM article
    WHERE article_category=2
    ORDER BY article_id DESC
    LIMIT 5
) UNION ALL (
    SELECT * FROM article
    WHERE article_category=3
    ORDER BY article_id DESC
    LIMIT 5
)
ORDER BY article_id DESC
LIMIT 5
// 执行时间：0.0261