數據庫小技巧：使用distinct去除重復行

這里有2個表

問題question表

 

 

樓層question_floor表

 

 

 

需求：已知某用戶的id為uid，實現“我的回復”功能，即查看我回復的所有問題

遇到的問題：如果直接對question表和question_floor表進行連接查詢的話，即

SELECT question.qid qid, question.uid uid, " +
        "question.ask_time, question.title, question.content, " +
        "question.current_floor, question.credit, question.is_resolved " +
        "FROM question, question_floor " +
        "WHERE question_floor.uid = #{uid} " +
        "AND question_floor.fid != 1 ORDER BY question.ask_time desc

當A多次回復帖子P時，A點擊"我的回復"按鈕，將會顯示多條帖子P的記錄。

解決方案：使用distinct

SELECT DISTINCT question.qid qid, question.uid uid, " +
        "question.ask_time, question.title, question.content, " +
        "question.current_floor, question.credit, question.is_resolved " +
        "FROM question, question_floor " +
        "WHERE question_floor.uid = #{uid} " +
        "AND question_floor.fid != 1 ORDER BY question.ask_time desc