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文档加密软件排名 sql工具有哪些

Excel是数据分析中最常用的工具  ， 利用Excel可以完成数据清洗 ， 预处理 ， 以及最常见的数据分类 ， 数据筛选 ， 分类汇总 ， 以及数据透视等操作 ， 而这些操作用SQL一样可以实现 。
SQL不仅可以从数据库中读取数据 ， 还能通过不同的SQL函数语句直接返回所需要的结果 ， 从而大大提高了自己在客户端应用程序中计算的效率 。
1 重复数据处理
查找重复记录 SELECt * FROM user Where (nick_name,password) in(SELECt nick_name,password FROM user group by nick_name,password having count(nick_name)>1);
查找去重记录 查找id更大的记录
SELECt * FROM user WHERe id in(SELECt max(id) FROM usergroup by nick_name,password having count(nick_name)>1);
删除重复记录 只保留id值最小的记录
DELETe c1FROM customer c1,customer c2WHERe c1.cust_email=c2.cust_emailAND c1.id>c2.id; DELETe FROM user Where (nick_name,password) in(SELECt nick_name,password FROM(SELECt nick_name,password FROM user group by nick_name,password having count(nick_name)>1) as tmp1)and id not in(SELECt id FROM(SELECt min(id) id FROM user group by nick_name,password having count(nick_name)>1) as tmp2);
2 缺失值处理 查找缺失值记录 SELECt * FROM customerWHERe cust_email IS ; 更新列填充空值
UPDATe sale set city = "未知" WHERe city IS ;UPDATE orderitems set price_new=IF(price_new,5.74); 查询并填充空值列
SELECT AVG(price_new) FROM orderitems;SELECt IF(price_new,5.74) AS bus_ifFROM orderitems;
3 计算列 更新表添加计算列 ALTER TABLE orderitems ADD price_new DECIMAL(8,2) NOT ;UPDATe orderitems set price_new= item_price*count;
查询计算列 SELECT item_price*count as sales FROM orderitems; 4 排序
多列排序 SELECt * FROM orderitemsORDER BY price_new DESC,quantity; 查询排名前几的记录
SELECt* FROM orderitemsORDER BY price_new DESC Limit 5; 查询第10大的值
SELECt DISTINCT price_newFROM orderitemsORDER BY price_new DESC LIMIT 9,1; 排名
数值相同的排名相同且排名连续
SELECt prod_price,(SELECT COUNT(DISTINCT prod_price)FROM productsWHERe prod_price>=a.prod_price) AS rankFROM products AS aORDER BY rank ;
5 字符串处理 字符串替换 UPDATe data1 SET city=REPLACE(city,'SH','shanghai');SELECT city FROM data1; 按位置字符串截取
字符串截取可用于数据分列
MySQL 字符串截取函数：left, right, substring, substring_index
SELECt left('example.com', 3); 从字符串的第 4 个字符位置开始取 ， 直到结束
SELECT substring('example.com', 4); 从字符串的第 4 个字符位置开始取 ， 只取 2 个字符
SELECT substring('example.com', 4, 2); 按关键字截取字符串
取之一个分隔符之前的所有字符 ， 结果是www
SELECT substring_index('www.google.com','.',1); 取倒数第二个分隔符之后的所有字符 ， 结果是google.com;
SELECT substring_index('www.google.com','.',-2); 6 筛选
通过操作符实现高级筛选 使用 AND OR IN NOT 等操作符实现高级筛选过滤
SELECT prod_name ， prod_price FROM ProductsWHERe vend_id IN('DLL01','BRS01');SELECt prod_name FROM Products WHERe NOT vend_id='DLL01'; 通配符筛选
常用通配符有% _ ^
SELECt * from customers WHERe country LIKE "CH%"; 7 表联结
SQL表连接可以实现类似于Excel中的Vlookup函数的功能
SELECt vend_id,prod_name,prod_priceFROM Vendors INNER JOIN ProductsON Vendors.vend_id=Products.vend_id;SELECt prod_name,vend_name,prod_price,quantityFROM OderItems,Products,VendorsWHERe Products.vend_id=Vendors.vend_idAND OrderItems.prod_id=Products.prod_idAND order_num=20007;
自联结 在一条SELECt语句中多次使用相同的表 SELECT c1.cust_od,c1.cust_name,c1.cust_contactFROM Customers as c1,Customers as c2WHERe c1.cust_name=c2.cust_nameAND c2.cust_contact='Jim Jones';
8 数据透视 数据分组可以实现Excel中数据透视表的功能
数据分组 group by 用于数据分组 having 用于分组后数据的过滤
SELECt order_num,COUNT(*) as itemsFROM OrderItemsGROUP BY order_num HAVINg COUNT(*)>=3;
交叉表 通过CASE WHEN函数实现
SELECt data1.city,CASE WHEN colour = "A" THEN price END AS A,CASE WHEN colour = "B" THEN price END AS B,CASE WHEN colour = "C" THEN price END AS C,CASE WHEN colour = "F" THEN price END AS FFROM data1 【文档加密软件排名 sql工具有哪些】注：以上代码在MySQL数据库中执行


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