MySQl 子查詢，左右串連，多表串連學習筆記，mysql學習筆記

MySQl 子查詢，左右串連，多表串連學習筆記，mysql學習筆記
1.子查詢是指在另一個查詢語句中的SELECT子句。

  例句：

  SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);


  其中，SELECT * FROM t1 ...稱為Outer Query[外查詢](或者Outer Statement),


  SELECT column1 FROM t2 稱為Sub Query[子查詢]。


  所以，我們說子查詢是嵌套在外查詢內部。而事實上它有可能在子查詢內部再嵌套子查詢。


  子查詢必須出現在圓括弧之間。
  


  行級子查詢


  SELECT * FROM t1 WHERE (col1,col2) = (SELECT col3, col4 FROM t2 WHERE id = 10);


  SELECT * FROM t1 WHERE ROW(col1,col2) = (SELECT col3, col4 FROM t2 WHERE id = 10);
  
  行級子查詢的返回結果最多為一行。


  最佳化子查詢






  -- 建立資料表


  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英寸膝上型電腦','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英寸遊戲本','遊戲本','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 ','台式機','聯想','3499',DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('Vostro 3800-R1206 台式電腦','台式機','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','台式機','蘋果','9188',DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('AT7-7414LP 台式電腦 （i5-3450四核 4G 500G 2G獨顯 DVD 鍵鼠 Linux ）','台式機','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','伺服器/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 T110 II伺服器','伺服器/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 專業級台式電腦','伺服器/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 頭戴顯示裝置','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機架式伺服器 2583i14','伺服器/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 頭戴顯示裝置','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);






-- 求所有電腦產品的平均價格,並且保留兩位小數，AVG,MAX,MIN、COUNT、SUM為彙總函式


   SELECT ROUND(AVG(goods_price),2) AS avg_price FROM tdb_goods;


-- 查詢所有價格大於平均價格的商品，並且按價格降序排序


   SELECT goods_id,goods_name,goods_price FROM tdb_goods WHERE goods_price > 5845.10 ORDER BY goods_price DESC;
  
-- 使用子查詢來實現


  SELECT goods_id,goods_name,goods_price FROM tdb_goods 




  WHERE goods_price > (SELECT ROUND(AVG(goods_price),2) AS avg_price FROM tdb_goods) 




  ORDER BY goods_price DESC;




-- 查詢類型為“超記本”的商品價格


 
   SELECT goods_price FROM tdb_goods WHERE goods_cate = '超級本';


-- 查詢價格大於或等於"超級本"價格的商品，並且按價格降序排列


 
   SELECT goods_id,goods_name,goods_price FROM tdb_goods 


   WHERE goods_price = ANY(SELECT goods_price FROM tdb_goods WHERE goods_cate = '超級本')


   ORDER BY goods_price DESC;
   


-- = ANY 或 = SOME 等價於 IN


   SELECT goods_id,goods_name,goods_price FROM tdb_goods 


   WHERE goods_price IN (SELECT goods_price FROM tdb_goods WHERE goods_cate = '超級本')


   ORDER BY goods_price DESC; 




-- 建立“商品分類”表




  CREATE TABLE IF NOT EXISTS tdb_goods_cates(


    cate_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    
    cate_name VARCHAR(40)


  );


-- 查詢tdb_goods表的所有記錄，並且按"類別"分組


  SELECT goods_cate FROM tdb_goods GROUP BY goods_cate;


-- 將分組結果寫入到tdb_goods_cates資料表


  INSERT tdb_goods_cates (cate_name) SELECT goods_cate FROM tdb_goods GROUP BY goods_cate;


-- 通過tdb_goods_cates資料表來更新tdb_goods表


  UPDATE tdb_goods INNER JOIN tdb_goods_cates ON goods_cate = cate_name 


  SET goods_cate = cate_id ;


-- 通過CREATE...SELECT來建立資料表並且同時寫入記錄
 
  -- SELECT brand_name FROM tdb_goods GROUP BY brand_name;


  CREATE TABLE tdb_goods_brands (


    brand_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,


    brand_name VARCHAR(40) NOT NULL


  ) SELECT brand_name FROM tdb_goods GROUP BY brand_name;




-- 通過tdb_goods_brands資料表來更新tdb_goods資料表(錯誤)


  UPDATE tdb_goods  INNER JOIN tdb_goods_brands ON brand_name = brand_name


  SET brand_name = brand_id;


  -- Column 'brand_name' in field list is ambigous


  -- 正確


  UPDATE tdb_goods AS  g  INNER JOIN tdb_goods_brands AS b ON g.brand_name = b.brand_name


  SET g.brand_name = b.brand_id;


-- 查看tdb_goods的資料表結構


  DESC tdb_goods;


-- 通過ALTER TABLE語句修改資料表結構




  ALTER TABLE tdb_goods  


  CHANGE goods_cate cate_id SMALLINT UNSIGNED NOT NULL,


  CHANGE brand_name brand_id SMALLINT UNSIGNED NOT NULL;
  
-- 分別在tdb_goods_cates和tdb_goods_brands表插入記錄


   INSERT tdb_goods_cates(cate_name) VALUES('路由器'),('交換器'),('網卡');


   INSERT tdb_goods_brands(brand_name) VALUES('海爾'),('清華同方'),('神舟');


-- 在tdb_goods資料表寫入任意記錄


   INSERT tdb_goods(goods_name,cate_id,brand_id,goods_price) VALUES(' LaserJet Pro P1606dn 黑白雷射印表機','12','4','1849');

-- 查詢所有商品的詳細資料(通過內串連實現)如下如：

   SELECT goods_id,goods_name,cate_name,brand_name,goods_price FROM tdb_goods AS g


   INNER JOIN tdb_goods_cates AS c ON g.cate_id = c.cate_id


   INNER JOIN tdb_goods_brands AS b ON g.brand_id = b.brand_id\G;

-- 查詢所有商品的詳細資料(通過左外串連實現)

   SELECT goods_id,goods_name,cate_name,brand_name,goods_price FROM tdb_goods AS g


   LEFT JOIN tdb_goods_cates AS c ON g.cate_id = c.cate_id


   LEFT JOIN tdb_goods_brands AS b ON g.brand_id = b.brand_id\G;

-- 查詢所有商品的詳細資料(通過右外串連實現)

   SELECT goods_id,goods_name,cate_name,brand_name,goods_price FROM tdb_goods AS g


   RIGHT JOIN tdb_goods_cates AS c ON g.cate_id = c.cate_id


   RIGHT JOIN tdb_goods_brands AS b ON g.brand_id = b.brand_id\G;


-- 無限分類的資料表設計


   CREATE TABLE tdb_goods_types(
     type_id   SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
     type_name VARCHAR(20) NOT NULL,
     parent_id SMALLINT UNSIGNED NOT NULL DEFAULT 0
  ); 


  INSERT tdb_goods_types(type_name,parent_id) VALUES('家用電器',DEFAULT);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('電腦、辦公',DEFAULT);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('大家電',1);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('生活電器',1);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('平板電視',3);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('空調',3);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('電風扇',4);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('飲水機',4);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('電腦整機',2);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('電腦配件',2);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('筆記本',9);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('超級本',9);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('遊戲本',9);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('CPU',10);
  INSERT tdb_goods_types(type_name,parent_id) VALUES('主機',10);


-- 尋找所有分類及其父類


  SELECT s.type_id,s.type_name,p.type_name FROM tdb_goods_types AS s LEFT JOIN tdb_goods_types AS  p ON s.parent_id = p.type_id;
   
-- 尋找所有分類及其子類


  SELECT p.type_id,p.type_name,s.type_name FROM tdb_goods_types AS p LEFT JOIN tdb_goods_types AS  s ON s.parent_id = p.type_id;


-- 尋找所有分類及其子類的數目


  SELECT p.type_id,p.type_name,count(s.type_name) AS children_count FROM tdb_goods_types AS p LEFT JOIN tdb_goods_types AS s ON s.parent_id = p.type_id GROUP BY p.type_name ORDER BY p.type_id;


-- 為tdb_goods_types添加child_count欄位


  ALTER TABLE tdb_goods_types ADD child_count MEDIUMINT UNSIGNED NOT NULL DEFAULT 0;


-- 將剛才查詢到的子類數量更新到tdb_goods_types資料表


  UPDATE tdb_goods_types AS t1 INNER JOIN ( SELECT p.type_id,p.type_name,count(s.type_name) AS children_count FROM tdb_goods_types AS p 


                                            LEFT JOIN tdb_goods_types AS s ON s.parent_id = p.type_id 
                             
                                            GROUP BY p.type_name 


                                            ORDER BY p.type_id ) AS t2 


  ON  t1.type_id = t2.type_id 


  SET t1.child_count = t2.children_count;




-- 複製編號為12,20的兩條記錄


  SELECT * FROM tdb_goods WHERE goods_id IN (19,20);




-- INSERT ... SELECT實現複製


  INSERT tdb_goods(goods_name,cate_id,brand_id) SELECT goods_name,cate_id,brand_id FROM tdb_goods WHERE goods_id IN (19,20);


-- 尋找重複記錄


  SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING count(goods_name) >= 2;


-- 重複資料刪除記錄


  DELETE t1 FROM tdb_goods AS t1 LEFT JOIN (SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING count(goods_name) >= 2 ) AS t2  ON t1.goods_name = t2.goods_name  WHERE t1.goods_id > t2.goods_id;


資料庫(比如MYSQL) ,表連結查詢與子查詢哪個效率高些? 為何

表串連查詢高啊。一般情況下，盡量不要用子查詢。
 
mysql40中一表關聯多表左串連sql寫法：

mysql4.0中一表關聯多表左串連sql寫法:
select m.zsbt,br.brand_name,b.bname from merchant m left join brand br on m.probrand=br.brand_id left join base_source b on m.zsdz=b.bid ;