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常用的比较运算符： =、>、<、>=、<=、<>、!=、<=>
修饰运算符
| 运算符 | 关键字 | 关键字 | 关键字 |
|---|---|---|---|
| ANY | SOME | ALL | |
、>= | 最小值 | 最小值 | 最大值 |
| <、<= | 最大值 | 最大值 | 最小值 |
| = | 任意值 | 任意值 | |
| <>、!= | 任意值 |
// 查找所有价格大于平均值的行mysql> SELECT goods_id,goods_name,goods_price FROM tdb_goods -> WHERE goods_price > (SELECT ROUND(AVG(goods_price)) FROM tdb_goods) -> ORDER BY goods_price;
运算符=ANY 和 =SOME 相当于 IN
=ANY =SOME --INmysql> 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');+----------+---------------------------------+-------------+| goods_id | goods_name | goods_price |+----------+---------------------------------+-------------+| 5 | X240(20ALA0EYCD) 12.5英寸超极本 | 4999.000 || 6 | U330P 13.3英寸超极本 | 4299.000 || 7 | SVP13226SCB 13.3英寸触控超极本 | 7999.000 |+----------+---------------------------------+-------------+
> ANY 表示大于最小值
// > ANY mysql> 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');+----------+----------------------------------+-------------+| goods_id | goods_name | goods_price |+----------+----------------------------------+-------------+| 2 | Y400N 14.0英寸笔记本电脑 | 4899.000 || 3 | G150TH 15.6英寸游戏本 | 8499.000 || 5 | X240(20ALA0EYCD) 12.5英寸超极本 | 4999.000 || 7 | SVP13226SCB 13.3英寸触控超极本 | 7999.000 || 13 | iMac ME086CH/A 21.5英寸一体电脑 | 9188.000 || 16 | PowerEdge T110 II服务器 | 5388.000 || 17 | Mac Pro MD878CH/A 专业级台式电脑 | 28888.000 || 18 | HMZ-T3W 头戴显示设备 | 6999.000 || 20 | X3250 M4机架式服务器 2583i14 | 6888.000 || 21 | HMZ-T3W 头戴显示设备 | 6999.000 |+----------+----------------------------------+-------------+
> ALL表示大于最大值
// > ALL mysql> SELECT goods_id,goods_name,goods_price FROM tdb_goods WHERE goods_price > ALL (SELECT goods_price FROM tdb_goods WHERE goods_cate='超级本');+----------+----------------------------------+-------------+| goods_id | goods_name | goods_price |+----------+----------------------------------+-------------+| 3 | G150TH 15.6英寸游戏本 | 8499.000 || 13 | iMac ME086CH/A 21.5英寸一体电脑 | 9188.000 || 17 | Mac Pro MD878CH/A 专业级台式电脑 | 28888.000 |+----------+----------------------------------+-------------+
NOT IN等效于！=ALL 或 <>ALL
// NOT IN 与 ！= ALL等效 ，以下查询不是超极本的电脑，两次查询的结果相同mysql> SELECT goods_id,goods_name,goods_price FROM tdb_goods WHERE goods_price NOT IN (SELECT goods_price FROM tdb_goods WHERE goods_cate='超级本');mysql> SELECT goods_id,goods_name,goods_price FROM tdb_goods WHERE goods_price != ALL (SELECT goods_price FROM tdb_goods WHERE goods_cate='超级本');+----------+------------------------------------------------------------------------+-------------+| goods_id | goods_name | goods_price |+----------+------------------------------------------------------------------------+-------------+| 1 | R510VC 15.6英寸笔记本 | 3399.000 || 2 | Y400N 14.0英寸笔记本电脑 | 4899.000 || 3 | G150TH 15.6英寸游戏本 | 8499.000 || 4 | X550CC 15.6英寸笔记本 | 2799.000 || 8 | iPad mini MD531CH/A 7.9英寸平板电脑 | 1998.000 || 9 | iPad Air MD788CH/A 9.7英寸平板电脑 （16G WiFi版） | 3388.000 || 10 | iPad mini ME279CH/A 配备 Retina 显示屏 7.9英寸平板电脑 （16G WiFi版） | 2788.000 || 11 | IdeaCentre C340 20英寸一体电脑 | 3499.000 || 12 | Vostro 3800-R1206 台式电脑 | 2899.000 || 13 | iMac ME086CH/A 21.5英寸一体电脑 | 9188.000 || 14 | AT7-7414LP 台式电脑 （i5-3450四核 4G 500G 2G独显 DVD 键鼠 Linux ） | 3699.000 || 15 | Z220SFF F4F06PA工作站 | 4288.000 || 16 | PowerEdge T110 II服务器 | 5388.000 || 17 | Mac Pro MD878CH/A 专业级台式电脑 | 28888.000 || 18 | HMZ-T3W 头戴显示设备 | 6999.000 || 19 | 商务双肩背包 | 99.000 || 20 | X3250 M4机架式服务器 2583i14 | 6888.000 || 21 | HMZ-T3W 头戴显示设备 | 6999.000 || 22 | 商务双肩背包 | 99.000 |+----------+------------------------------------------------------------------------+-------------+
如果子查询返回任何行，EXISTS将返回TRUE ，否则返回FALSE
select * from t1 where exists (select * from t1 where id = 2);
使用查询插入数据表
创建分类表，用以上语句更新分类表
mysql> INSERT INTO tdb_goods_cate (cate_name) SELECT goods_cate FROM tdb_goods GROUP BY goods_cate;
UPDATE tbl_name1 [LEFT|RIGHT]JOIN tbl_name2 ON condition SET name=value… WHERE condition..
// 按照分类表，将商品表中的数据更新mysql> UPDATE tdb_goods INNER JOIN tdb_goods_cate ON tdb_goods.goods_cate=tdb_goods_cate.cate_name SET tdb_goods.goods_cate = tdb_goods_cate.id;
CREATE TABLE [IF NOT EXISTS] tbl_name [(create_defition,…)] select_statement…
// 创建表的同时插入表信息mysql> CREATE TABLE tdb_goods_brand( -> id INT(5) UNSIGNED PRIMARY KEY AUTO_INCREMENT, -> brand_name VARCHAR(40) -> ) -> SELECT brand_name FROM tdb_goods GROUP BY brand_name;
RIGHT [OUUTER] JOIN ： 右外连接，显示右表的所有记录和左表中满足条件的记录
在MySQL中，JOIN,CROSS JOIN 和INNER JOIN 是等价的
mysql> SELECT goods_id,goods_name,cate_name,brand_name,goods_price,is_show ,is_saleoff
-> FROM tdb_goods g -> JOIN tdb_goods_cate c on c.id = g.goods_cate_id -> JOIN tdb_goods_brand b on b.id = g.brand_id;// 多表查询mysql> SELECT goods_id,goods_name,cate_name,brand_name,goods_price,is_show ,is_saleoff FROM tdb_goods INNER JOIN tdb_goods_cate ON tdb_goods.goods_cate_id = tdb_goods_cate.id INNER JOIN tdb_goods_brand ON tdb_goods.brand_id = tdb_goods_brand.id;// 使用AS未每个表重命名mysql> SELECT goods_id,goods_name,cate_name,brand_name,goods_price,is_show ,is_saleoff -> FROM tdb_goods g -> JOIN tdb_goods_cate c on c.id = g.goods_cate_id -> JOIN tdb_goods_brand b on b.id = g.brand_id;// 结果相同+----------+------------------------------------------------------------------------+---------------+------------+-------------+---------+------------+| goods_id | goods_name | cate_name | brand_name | goods_price | is_show | is_saleoff |+----------+------------------------------------------------------------------------+---------------+------------+-------------+---------+------------+| 1 | R510VC 15.6英寸笔记本 | 笔记本 | 华硕 | 3399.000 | 1 | 0 || 2 | Y400N 14.0英寸笔记本电脑 | 笔记本 | 联想 | 4899.000 | 1 | 0 || 3 | G150TH 15.6英寸游戏本 | 游戏本 | 雷神 | 8499.000 | 1 | 0 || 4 | X550CC 15.6英寸笔记本 | 笔记本 | 华硕 | 2799.000 | 1 | 0 || 5 | X240(20ALA0EYCD) 12.5英寸超极本 | 超级本 | 联想 | 4999.000 | 1 | 0 || 6 | U330P 13.3英寸超极本 | 超级本 | 联想 | 4299.000 | 1 | 0 || 7 | SVP13226SCB 13.3英寸触控超极本 | 超级本 | 索尼 | 7999.000 | 1 | 0 || 8 | iPad mini MD531CH/A 7.9英寸平板电脑 | 平板电脑 | 苹果 | 1998.000 | 1 | 0 || 9 | iPad Air MD788CH/A 9.7英寸平板电脑 （16G WiFi版） | 平板电脑 | 苹果 | 3388.000 | 1 | 0 || 10 | 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 | 2788.000 | 1 | 0 || 11 | IdeaCentre C340 20英寸一体电脑 | 台式机 | 联想 | 3499.000 | 1 | 0 || 12 | Vostro 3800-R1206 台式电脑 | 台式机 | 戴尔 | 2899.000 | 1 | 0 || 13 | iMac ME086CH/A 21.5英寸一体电脑 | 台式机 | 苹果 | 9188.000 | 1 | 0 || 14 | AT7-7414LP 台式电脑 （i5-3450四核 4G 500G 2G独显 DVD 键鼠 Linux ） | 台式机 | 宏碁 | 3699.000 | 1 | 0 || 15 | Z220SFF F4F06PA工作站 | 服务器/工作站 | 惠普 | 4288.000 | 1 | 0 || 16 | PowerEdge T110 II服务器 | 服务器/工作站 | 戴尔 | 5388.000 | 1 | 0 || 17 | Mac Pro MD878CH/A 专业级台式电脑 | 服务器/工作站 | 苹果 | 28888.000 | 1 | 0 || 18 | HMZ-T3W 头戴显示设备 | 笔记本配件 | 索尼 | 6999.000 | 1 | 0 || 19 | 商务双肩背包 | 笔记本配件 | 索尼 | 99.000 | 1 | 0 || 20 | X3250 M4机架式服务器 2583i14 | 服务器/工作站 | IBM | 6888.000 | 1 | 0 || 21 | HMZ-T3W 头戴显示设备 | 笔记本配件 | 索尼 | 6999.000 | 1 | 0 || 22 | 商务双肩背包 | 笔记本配件 | 索尼 | 99.000 | 1 | 0 |+----------+------------------------------------------------------------------------+---------------+------------+-------------+---------+------------+
无限分组：
// 使用左连接查询每个子类的父类mysql> SELECT s.type_id AS son_id, s.type_name AS son_name,p.type_name AS parent_name -> FROM tdb_goods_types AS s LEFT JOIN tdb_goods_types AS p -> ON s.parent_id = p.type_id;+--------+------------+-------------+| son_id | son_name | parent_name |+--------+------------+-------------+| 1 | 家用电器 | NULL || 2 | 电脑、办公 | NULL || 3 | 大家电 | 家用电器 || 4 | 生活电器 | 家用电器 || 5 | 平板电视 | 大家电 || 6 | 空调 | 大家电 || 7 | 电风扇 | 生活电器 || 8 | 饮水机 | 生活电器 || 9 | 电脑整机 | 电脑、办公 || 10 | 电脑配件 | 电脑、办公 || 11 | 笔记本 | 电脑整机 || 12 | 超级本 | 电脑整机 || 13 | 游戏本 | 电脑整机 || 14 | CPU | 电脑配件 || 15 | 主机 | 电脑配件 |+--------+------------+-------------+
使用左查询查询所有父类的子类mysql> SELECT p.type_id parent_id, p.type_name parent_name, s.type_name son_name -> FROM tdb_goods_types AS p LEFT JOIN tdb_goods_types AS s -> ON p.type_id = s.parent_id -> ORDER BY parent_id;+-----------+-------------+----------+| parent_id | parent_name | son_name |+-----------+-------------+----------+| 1 | 家用电器 | 大家电 || 1 | 家用电器 | 生活电器 || 2 | 电脑、办公 | 电脑整机 || 2 | 电脑、办公 | 电脑配件 || 3 | 大家电 | 平板电视 || 3 | 大家电 | 空调 || 4 | 生活电器 | 电风扇 || 4 | 生活电器 | 饮水机 || 5 | 平板电视 | NULL || 6 | 空调 | NULL || 7 | 电风扇 | NULL || 8 | 饮水机 | NULL || 9 | 电脑整机 | 笔记本 || 9 | 电脑整机 | 游戏本 || 9 | 电脑整机 | 超级本 || 10 | 电脑配件 | 主机 || 10 | 电脑配件 | CPU || 11 | 笔记本 | NULL || 12 | 超级本 | NULL || 13 | 游戏本 | NULL || 14 | CPU | NULL || 15 | 主机 | NULL |+-----------+-------------+----------+// 查看父类的子类个数mysql> SELECT p.type_id AS parent_id, p.type_name AS parent_name, count(p.parent_id) AS son_count -> FROM tdb_goods_types AS p LEFT JOIN tdb_goods_types AS s -> ON p.type_id = s.parent_id -> GROUP BY parent_name ORDER BY parent_id;+-----------+-------------+-----------+| parent_id | parent_name | son_count |+-----------+-------------+-----------+| 1 | 家用电器 | 2 || 2 | 电脑、办公 | 2 || 3 | 大家电 | 2 || 4 | 生活电器 | 2 || 5 | 平板电视 | 1 || 6 | 空调 | 1 || 7 | 电风扇 | 1 || 8 | 饮水机 | 1 || 9 | 电脑整机 | 3 || 10 | 电脑配件 | 2 || 11 | 笔记本 | 1 || 12 | 超级本 | 1 || 13 | 游戏本 | 1 || 14 | CPU | 1 || 15 | 主机 | 1 |+-----------+-------------+-----------+
DELETE tbl_name1,tbl_name2.. FROM table_references WHERE condidtions
同时删除多个表的记录
DELETE t1,t2 FROM t1,t2 WHERE t1.name = t2.name;
使用多表删除删除表中的重复数据
// 先用group by删选出名称相同的数量大于2的分组，筛选出的分组既是需要删除的记录SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING count(goods_name) >= 2+----------+-----------------------+| goods_id | goods_name |+----------+-----------------------+| 18 | HMZ-T3W 头戴显示设备 || 19 | 商务双肩背包 |+----------+-----------------------+// 将上表与原表内连接，mysql> SELECT * FROM tdb_goods AS t1 -> INNER 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 ;+----------+-----------------------+---------------+----------+-------------+---------+------------+----------+-----------------------+| goods_id | goods_name | goods_cate_id | brand_id | goods_price | is_show | is_saleoff | goods_id | goods_name |+----------+-----------------------+---------------+----------+-------------+---------+------------+----------+-----------------------+| 18 | HMZ-T3W 头戴显示设备 | 37 | 6 | 6999.000 | 1 | 0 | 18 | HMZ-T3W 头戴显示设备 || 19 | 商务双肩背包 | 37 | 6 | 99.000 | 1 | 0 | 19 | 商务双肩背包 || 21 | HMZ-T3W 头戴显示设备 | 37 | 6 | 6999.000 | 1 | 0 | 18 | HMZ-T3W 头戴显示设备 || 22 | 商务双肩背包 | 37 | 6 | 99.000 | 1 | 0 | 19 | 商务双肩背包 |+----------+-----------------------+---------------+----------+-------------+---------+------------+----------+-----------------------+// 最后删除重复的记录DELETE t1 FROM tdb_goods AS t1 INNER 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;