您需要GROUP BY始终相同的列。
剩下的是一个带有condothion的聚合函数
这叫做支点或翻转

SELECT
CONCAT(
    'https://example.com/?search=',
    comment_content
) AS link,
wp_comments.user_id,
user_email,
user_login,
user_nicename,
comment_date as 'Interview Date',
display_name,
user_registered,
MAX(CASE WHEN meta_key = 'first_name' THEN meta_value END) as 'first_name', 
MAX(CASE WHEN meta_key = 'last_name' THEN meta_value END) as 'last_name', 
MAX(CASE WHEN meta_key = 'user_birthday' THEN meta_value END) as 'user_brthday' 
MAX(CASE WHEN meta_key = 'user_sex' THEN meta_value END) as 'user_sex' 
FROM ...
WHERE ....
GROUP BY link,wp_comments.user_id,
user_email,
user_login,
user_nicename,
`Interview Date`,
display_name,
user_registered