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SQL是什么工具 sqlserver工具有哪些

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SQL是什么工具 sqlserver工具有哪些

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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 重復數據處理
查找重復記錄
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);刪除重復記錄只保留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);查詢并填充空值列
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;【SQL是什么工具 sqlserver工具有哪些】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
字符串截取可用于數據分列
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后的所有字符，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于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 用于數據分組 having 用于分組后數據的過濾
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注：以上代碼在MySQL數據庫中執行