Mysql子查询，连接，多表更新

1.子查询是指在另一个查询语句中的SELECT子句。

例句：

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

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

SELECT column1 FROM t2 称为Sub Query[子查询]。

所以，我们说子查询是嵌套在外查询内部。而事实上它有可能在子查询内部再嵌套子查询。

子查询必须出现在圆括号之间。

行级子查询

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);

行级子查询的返回结果最多为一行。

优化子查询

 

-- 创建数据表

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
);

-- 写入记录

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'R510VC 15.6英寸笔记本\',\'笔记本\',\'华硕\',\'3399\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'Y400N 14.0英寸笔记本电脑\',\'笔记本\',\'联想\',\'4899\',DEFAULT,DEFAULT);

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

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'X550CC 15.6英寸笔记本\',\'笔记本\',\'华硕\',\'2799\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'X240(20ALA0EYCD) 12.5英寸超极本\',\'超级本\',\'联想\',\'4999\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'U330P 13.3英寸超极本\',\'超级本\',\'联想\',\'4299\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'SVP13226SCB 13.3英寸触控超极本\',\'超级本\',\'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英寸平板电脑\',\'平板电脑\',\'苹果\',\'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英寸平板电脑 （16G WiFi版）\',\'平板电脑\',\'苹果\',\'3388\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\' iPad mini ME279CH/A 配备 Retina 显示屏 7.9英寸平板电脑 （16G WiFi版）\',\'平板电脑\',\'苹果\',\'2788\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'IdeaCentre C340 20英寸一体电脑 \',\'台式机\',\'联想\',\'3499\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'Vostro 3800-R1206 台式电脑\',\'台式机\',\'戴尔\',\'2899\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'iMac ME086CH/A 21.5英寸一体电脑\',\'台式机\',\'苹果\',\'9188\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'AT7-7414LP 台式电脑 （i5-3450四核 4G 500G 2G独显 DVD 键鼠 Linux ）\',\'台式机\',\'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\',\'服务器/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服务器\',\'服务器/工作站\',\'戴尔\',\'5388\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'Mac Pro MD878CH/A 专业级台式电脑\',\'服务器/工作站\',\'苹果\',\'28888\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\' HMZ-T3W 头戴显示设备\',\'笔记本配件\',\'索尼\',\'6999\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'商务双肩背包\',\'笔记本配件\',\'索尼\',\'99\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'X3250 M4机架式服务器 2583i14\',\'服务器/工作站\',\'IBM\',\'6888\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'玄龙精英版 笔记本散热器\',\'笔记本配件\',\'九州风神\',\'\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\' HMZ-T3W 头戴显示设备\',\'笔记本配件\',\'索尼\',\'6999\',DEFAULT,DEFAULT);

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(\'商务双肩背包\',\'笔记本配件\',\'索尼\',\'99\',DEFAULT,DEFAULT);

 

-- 求所有电脑产品的平均价格,并且保留两位小数，AVG,MAX,MIN、COUNT、SUM为聚合函数

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

-- 查询所有价格大于平均价格的商品，并且按价格降序排序

SELECT goods_id,goods_name,goods_price FROM tdb_goods WHERE goods_price > 5845.10 ORDER BY goods_price DESC;

-- 使用子查询来实现

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;

-- 查询类型为“超记本”的商品价格

SELECT goods_price FROM tdb_goods WHERE goods_cate = \'超级本\';

-- 查询价格大于或等于"超级本"价格的商品，并且按价格降序排列

SELECT goods_id,goods_name,goods_price FROM tdb_goods

WHERE goods_price = ANY(SELECT goods_price FROM tdb_goods WHERE goods_cate = \'超级本\')

ORDER BY goods_price DESC;

-- = ANY 或 = SOME 等价于 IN

SELECT goods_id,goods_name,goods_price FROM tdb_goods

WHERE goods_price IN (SELECT goods_price FROM tdb_goods WHERE goods_cate = \'超级本\')

ORDER BY goods_price DESC;

-- 创建“商品分类”表

CREATE TABLE IF NOT EXISTS tdb_goods_cates(

cate_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,

cate_name VARCHAR(40)

);

-- 查询tdb_goods表的所有记录，并且按"类别"分组

SELECT goods_cate FROM tdb_goods GROUP BY goods_cate;

-- 将分组结果写入到tdb_goods_cates数据表

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

-- 通过tdb_goods_cates数据表来更新tdb_goods表

UPDATE tdb_goods INNER JOIN tdb_goods_cates ON goods_cate = cate_name

SET goods_cate = cate_id ;

-- 通过CREATE...SELECT来创建数据表并且同时写入记录

-- 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;

-- 通过tdb_goods_brands数据表来更新tdb_goods数据表(错误)

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

-- 正确

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的数据表结构

DESC tdb_goods;

-- 通过ALTER TABLE语句修改数据表结构

ALTER TABLE tdb_goods

CHANGE goods_cate cate_id SMALLINT UNSIGNED NOT NULL,

CHANGE brand_name brand_id SMALLINT UNSIGNED NOT NULL;

-- 分别在tdb_goods_cates和tdb_goods_brands表插入记录

INSERT tdb_goods_cates(cate_name) VALUES(\'路由器\'),(\'交换机\'),(\'网卡\');

INSERT tdb_goods_brands(brand_name) VALUES(\'海尔\'),(\'清华同方\'),(\'神舟\');

-- 在tdb_goods数据表写入任意记录

INSERT tdb_goods(goods_name,cate_id,brand_id,goods_price) VALUES(\' LaserJet Pro P1606dn 黑白激光打印机\',\'12\',\'4\',\'1849\');

-- 查询所有商品的详细信息(通过内连接实现)

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;

-- 查询所有商品的详细信息(通过左外连接实现)

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;

-- 查询所有商品的详细信息(通过右外连接实现)

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;

-- 无限分类的数据表设计

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(\'家用电器\',DEFAULT);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'电脑、办公\',DEFAULT);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'大家电\',1);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'生活电器\',1);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'平板电视\',3);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'空调\',3);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'电风扇\',4);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'饮水机\',4);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'电脑整机\',2);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'电脑配件\',2);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'笔记本\',9);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'超级本\',9);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'游戏本\',9);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'CPU\',10);
INSERT tdb_goods_types(type_name,parent_id) VALUES(\'主机\',10);

-- 查找所有分类及其父类

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;

-- 查找所有分类及其子类

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;

-- 查找所有分类及其子类的数目

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;

-- 为tdb_goods_types添加child_count字段

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

-- 将刚才查询到的子类数量更新到tdb_goods_types数据表

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;

-- 复制编号为12,20的两条记录

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

-- INSERT ... SELECT实现复制

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);

-- 查找重复记录

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

-- 删除重复记录

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;