《PHP實戰：mysql查找刪除重復數據并只保留一條實例詳解》要點：
本文介紹了PHP實戰：mysql查找刪除重復數據并只保留一條實例詳解，希望對您有用。如果有疑問，可以聯系我們。
有這樣一張表,表數據及結果如下：PHP實戰
| school_id | school_name | total_student | test_takers |
| 1239 | Abraham Lincoln High School | 55 | 50 |
| 1240 | Abraham Lincoln High School | 70 | 35 |
| 1241 | Acalanes High School | 120 | 89 |
| 1242 | Academy Of The Canyons | 30 | 30 |
| 1243 | Agoura High School | 89 | 40 |
| 1244 | Agoura High School | 100 | 50 |
我們可以看出,school_name的字段值有重復數據(Abraham Lincoln High School 和Agoura High School分別出現兩次),那么如何刪除這兩條數據,從而只讓這兩個數值出現一次呢? 具體實現方法如下：PHP實戰
1、刪除重復記錄,保存Id最小的一條PHP實戰
delete FROM `test` WHERE `school_name` in (SELECT `school_name` FROM `test` GROUP BY `school_name` HAVING COUNT( * ) >1) and school_id not in (select min(school_id) from test group by school_id having count(* )>1)
先使用GROUP BY having語法查詢出重復的數據,然后刪除重復數據并保留school_id最小的一條.PHP實戰
2、刪除重復記錄,保存Id最大的一條PHP實戰
delete FROM `test` WHERE `school_name` in (SELECT `school_name` FROM `test` GROUP BY `school_name` HAVING COUNT( * ) >1) and school_id not in (select max(school_id) from test group by school_id having count(* )>1)
原理和上面一樣.PHP實戰
以上就是mysql查找刪除重復數據并只保留一條實例詳解,希望能幫助到大家,謝謝大家對本站的支持!PHP實戰
