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2023-12-09
小编给大家分享一下mysql子查询语句怎么写,希望大家阅读完这篇文章之后都有所收获,下面让我们一起去探讨吧!
mysql子查询语句是指在另一个查询语句中的SELECT子句,例句如“SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);”。
本文操作环境:Windows7系统、mysql5.7版、Dell G3电脑。
mysql 子查询语句:
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) = (SELECTcol3, col4FROM 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 KEYAUTO_INCREMENT, goods_nameVARCHAR(150) NOT NULL, goods_cate VARCHAR(40) NOT NULL, brand_nameVARCHAR(40) NOT NULL, goods_price DECIMAL(15,3) UNSIGNED NOT NULL DEFAULT 0, is_showBOOLEAN 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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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
SELECTgoods_id,goods_name,goods_priceFROM 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) ASavg_priceFROM 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 WHEREgoods_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 WHEREgoods_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 (SELECTgoods_priceFROM tdb_goods WHERE goods_cate = 超级本) ORDER BY goods_price DESC;-- 创建“商品分类”表
CREATE TABLE IF NOT EXISTStdb_goods_cates( cate_idSMALLINT UNSIGNED PRIMARY KEYAUTO_INCREMENT, cate_nameVARCHAR(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 BYgoods_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 ONgoods_cate = cate_nameSET 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 UNSIGNEDPRIMARYKEY AUTO_INCREMENT, brand_name VARCHAR(40) NOT NULL ) SELECT brand_name FROM tdb_goods GROUP BYbrand_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 ONbrand_name = brand_nameSET brand_name = brand_id; -- Column brand_name in field list is ambigous-- 正确
UPDATEtdb_goodsAS 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); INSERTtdb_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
INSERTtdb_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)
SELECTgoods_id,goods_name,cate_name,brand_name,goods_priceFROM 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)
SELECTgoods_id,goods_name,cate_name,brand_name,goods_priceFROM tdb_goods AS g LEFT JOIN tdb_goods_cates AS c ONg.cate_id = c.cate_idLEFT 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)
SELECTgoods_id,goods_name,cate_name,brand_name,goods_priceFROM tdb_goods AS g RIGHT JOIN tdb_goods_cates AS c ONg.cate_id = c.cate_idRIGHT 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 TABLEtdb_goods_types( type_idSMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT, type_name VARCHAR(20) NOT NULL, parent_id SMALLINT UNSIGNED NOT NULL DEFAULT 0 ); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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); INSERTtdb_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
SELECTp.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 ONs.parent_id = p.type_idGROUP 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 BYp.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
INSERTtdb_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
SELECTgoods_id,goods_nameFROM 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 ONt1.goods_name = t2.goods_nameWHERE t1.goods_id > t2.goods_id;看完了这篇文章,相信你对“mysql子查询语句怎么写”有了一定的了解,如果想了解更多相关知识,欢迎关注行业资讯频道,感谢各位的阅读!
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