數據庫刪除重復數據

               當數據庫數據量大的時候，刪除重復元素是很討厭的，有時候怎么也寫不對，閑下來整理一下刪除
         重復數據的sql，數據表是之前看mysql教學視頻的素材，但是找不到哪里的了，如果原作者看到請
         留言。

    -- 創建數據表

    CREATE TABLE IF NOT EXISTS tdb_goods(
        goods_id    SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
        goods_name  VARCHAR(150) NOT NULL,
        goods_cate  VARCHAR(40)  NOT NULL,
        brand_name  VARCHAR(40)  NOT NULL,
        goods_price DECIMAL(15,3) UNSIGNED NOT NULL DEFAULT 0,
        is_show     BOOLEAN NOT NULL DEFAULT 1,
        is_saleoff  BOOLEAN NOT NULL DEFAULT 0
    );

 -- 寫入記錄

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('R510VC 15.6英寸筆記本','筆記本','華碩','3399',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('Y400N 14.0英寸筆記本電腦','筆記本','聯想','4899',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('G150TH 15.6英寸游戲本','游戲本','雷神','8499',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('X550CC 15.6英寸筆記本','筆記本','華碩','2799',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('X240(20ALA0EYCD) 12.5英寸超極本','超級本','聯想','4999',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('U330P 13.3英寸超極本','超級本','聯想','4299',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('SVP13226SCB 13.3英寸觸控超極本','超級本','索尼','7999',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('iPad mini MD531CH/A 7.9英寸平板電腦','平板電腦','蘋果','1998',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('iPad Air MD788CH/A 9.7英寸平板電腦 （16G WiFi版）','平板電腦','蘋果','3388',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) 
 VALUES(' iPad mini ME279CH/A 配備 Retina 顯示屏 7.9英寸平板電腦 （16G WiFi版）','平板電腦',
 '蘋果','2788',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('IdeaCentre C340 20英寸一體電腦 ','臺式機','聯想','3499',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('Vostro 3800-R1206 臺式電腦','臺式機','戴爾','2899',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('iMac ME086CH/A 21.5英寸一體電腦','臺式機','蘋果','9188',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('AT7-7414LP 臺式電腦 （i5-3450四核 4G 500G 2G獨顯 DVD 鍵鼠 Linux ）','臺式機',
 '宏碁','3699',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('Z220SFF F4F06PA工作站','服務器/工作站','惠普','4288',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('PowerEdge ×××10 II服務器','服務器/工作站','戴爾','5388',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('Mac Pro MD878CH/A 專業級臺式電腦','服務器/工作站','蘋果','28888',
 DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) 
 VALUES(' HMZ-T3W 頭戴顯示設備','筆記本配件','索尼','6999',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('商務雙肩背包','筆記本配件','索尼','99',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('X3250 M4機架式服務器 2583i14','服務器/工作站','IBM','6888',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('玄龍精英版 筆記本散熱器','筆記本配件','九州風神','',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) 
 VALUES(' HMZ-T3W 頭戴顯示設備','筆記本配件','索尼','6999',DEFAULT,DEFAULT);

 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff)
 VALUES('商務雙肩背包','筆記本配件','索尼','99',DEFAULT,DEFAULT);

 --插入重復數據
 INSERT tdb_goods(goods_name,cate_id,brand_id) 
 SELECT goods_name,cate_id,brand_id,goods_price FROM tdb_goods
 WHERE goods_id IN (19,20)

 --查詢重復數據
 SELECT goods_id,goods_name,goods_price FROM tdb_goods 
 GROUP BY goods_name,goods_price HAVING count(goods_name) >= 2

 --將要刪除的id查詢出來
 select t1.goods_id from  tdb_goods as t1 left  JOIN
 (SELECT goods_id,goods_name,goods_price FROM tdb_goods 
 GROUP BY goods_name,goods_price HAVING count(goods_name) >= 2) t2 
 on t1.goods_name = t2.goods_name where t1.goods_id>t2.goods_id

    --執行刪除
delete t1 from  tdb_goods as t1 left  JOIN 
(SELECT goods_id,goods_name,goods_price FROM tdb_goods 
GROUP BY goods_name,goods_price HAVING count(goods_name) >= 2) t2 
on t1.goods_name = t2.goods_name 
where t1.goods_id>t2.goods_id