Mysql & gt; query statement

Mysql> query statement * query multiple unique records with id 1 a 2 B 3 c 4 c 5 bselect id, name from s1 group by name1 a2 b3 c5 B * query records with the most repeated records SELECT keyword, count (*) AS count FROM article_keyword group by keyword order by count desc limit 20 * query repeat records and repeat Times select user_name, count (*) as count from user_table group by user_name having count> 1; * multi-join query s1 table id name3 a s2 table id s1_id age 1 2 122 3 23 SELECT * FROM 's2 'where 's1 _ id' = (SELECT id FROM 's1 'where' name' = 'A '); result 2 3 23