文檔加密軟件排名：sql工具有哪些

Excel是數據分析中最常用的工具 ，利用Excel可以完成數據清洗，預處理，以及最常見的數據分類，數據篩選，分類匯總，以及數據透視等操作，而這些操作用SQL一樣可以實現。

SQL不僅可以從數據庫中讀取數據，還能通過不同的SQL函數語句直接返回所需要的結果，從而大大提高了自己在客戶端應用程序中計算的效率。

1 重複數據處理

查找重複記錄

SELECT * FROM user Where (nick_name,password) in(SELECT nick_name,password FROM user group by nick_name,password having count(nick_name)>1);

查找去重記錄

查找id最大的記錄

SELECT * FROM user WHERE id in(SELECT max(id) FROM usergroup by nick_name,password having count(nick_name)>1);

刪除重複記錄

只保留id值最小的記錄

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 缺失值處理

查找缺失值記錄

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);

查詢並填充空值列

SELECT AVG(price_new) FROM orderitems;SELECT IF(price_new,5.74) AS bus_ifFROM orderitems;

3 計算列

更新表添加計算列

ALTER TABLE orderitems ADD price_new DECIMAL(8,2) NOT ;UPDATE orderitems set price_new= item_price*count;

查詢計算列

SELECT item_price*count as sales FROM orderitems;

4 排序

多列排序

SELECT * FROM orderitemsORDER BY price_new DESC,quantity;

查詢排名前幾的記錄

SELECT  * FROM orderitemsORDER BY price_new DESC Limit 5;

查詢第10大的值

SELECT DISTINCT price_newFROM orderitemsORDER BY price_new DESC LIMIT 9,1;

排名

數值相同的排名相同且排名連續

SELECT prod_price,(SELECT COUNT(DISTINCT prod_price)FROM productsWHERE prod_price>=a.prod_price) AS rankFROM products AS aORDER BY rank ;

5 字符串處理

字符串替換

UPDATE data1 SET city=REPLACE(city,'SH','shanghai');SELECT city FROM data1;

按位置字符串截取

字符串截取可用於數據分列

MySQL 字符串截取函數：left, right, substring, substring_index

SELECT left('example.com', 3);

從字符串的第 4 個字符位置開始取，直到結束

SELECT substring('example.com', 4);

從字符串的第 4 個字符位置開始取，只取 2 個字符

SELECT substring('example.com', 4, 2);

按關鍵字截取字符串

取第一個分隔符之前的所有字符，結果是www

SELECT substring_index('www.google.com','.',1);

取倒數第二個分隔符之後的所有字符，結果是google.com;

SELECT substring_index('www.google.com','.',-2);

6 篩選

通過操作符實現高級篩選

使用 AND OR IN NOT 等操作符實現高級篩選過濾

SELECT prod_name，prod_price FROM ProductsWHERE vend_id IN('DLL01','BRS01');SELECT prod_name FROM Products WHERE NOT vend_id='DLL01';

通配符篩選

常用通配符有% _ ^

SELECT * from customers WHERE country LIKE "CH%";

7 表聯結

SQL表連接可以實現類似於Excel中的Vlookup函數的功能

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;

自聯結 在一條SELECT語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 數據透視

數據分組可以實現Excel中數據透視表的功能

數據分組

group by 用於數據分組 having 用於分組後數據的過濾

SELECT order_num,COUNT(*) as itemsFROM OrderItemsGROUP BY order_num HAVING COUNT(*)>=3;

交叉表

通過CASE WHEN函數實現

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

註：以上代碼在MySQL數據庫中執行