which is the best / efficient way to execute MySQL query - mysql

Question

1st approach :-
SELECT
clipComment.commentId,
clipComment.commentedBy,
clipComment.clipId AS commentTypeId,
'clip' AS commentType,
clipComment.commentDescription,
clipComment.commentCreatedDateTime,
clipComment.commentModifiedDateTime,
clipComment.commentLikeCount,
userProfile.userName,
userProfile.firstName,
userProfile.LastName,
userProfile.profilePicUrl,
userProfile.themeForeground,
userProfile.themeBackground,
IF(derCommentLike.commentId = clipComment.commentId,
1,
0) likedByMe
FROM
clipComment
LEFT JOIN
(SELECT
*
FROM
clipCommentLikes
WHERE
commentLikedBy = 16) derCommentLike
ON
derCommentLike.commentId = clipComment.commentId
LEFT JOIN
userProfile
ON
userProfile.userId = clipComment.commentedBy
WHERE
clipComment.clipId = 141
2nd approach :-
SELECT
clipComment.commentId,
clipComment.commentedBy,
clipComment.clipId AS commentTypeId,
'clip' AS commentType,
clipComment.commentDescription,
clipComment.commentCreatedDateTime,
clipComment.commentModifiedDateTime,
clipComment.commentLikeCount,
userProfile.userName,
userProfile.firstName,
userProfile.LastName,
userProfile.profilePicUrl,
userProfile.themeForeground,
userProfile.themeBackground,
IF( derCommentLike.commentId = clipComment.commentId , 1 , 0 ) AS likedByMe
FROM
(SELECT
*
FROM
clipCommentLikes
WHERE
commentLikedBy = 16) derCommentLike
RIGHT OUTER JOIN clipComment
ON derCommentLike.commentId = clipComment.commentId
RIGHT OUTER JOIN userProfile
ON clipComment.commentedBy = userProfile.userId
WHERE
clipComment.clipId = 141
both query returns same result, but just want to know which approach should i follow & which one is more efficient to follow. record set will contain millions of record, so i want to use best way. or i am doing work then please correct me. thank you in advance.
explain statement 1st approach
explain statement 2nd approach
explain statement 1st approach

Answer 1

IF(derCommentLike.commentId = clipComment.commentId, 1, 0) likedByMe
...
LEFT JOIN
(SELECT *
FROM clipCommentLikes
WHERE commentLikedBy = 16
) derCommentLike
ON derCommentLike.commentId = clipComment.commentId
-->
( EXISTS SELECT * FROM clipCommentLikes
WHERE commentId = clipComment.commentId
) AS likedByMe
Explanation:
JOIN ( SELECT ... ) has no index to make it efficient
LEFT JOIN ( ... ) begs for evaluating the subquery after the left table, thereby begging for the subquery to be evaluated repeatedly.
SELECT * (in your subquery) is gathering lots of stuff that is not used. (SELECT * in EXISTS does not mean to fetch everything; the * is just a place holder.)
EXISTS evaluates to 1 (true) or 0 (false), which seems to be what you want.