实战派mysql高阶应用指南_MySQL高阶SQL语句（学会这些，让你对于数据库游刃有余）_Gengchenchen的博客-CSDN博客...
------GROUP BY------對(duì)GROUP BY后面的欄位的查詢(xún)結(jié)果進(jìn)行匯總分組，通常是結(jié)合聚合函數(shù)一起使用的
GROUP BY 有一個(gè)原則，就是 SELECT 后面的所有列中，沒(méi)有使用聚合函數(shù)的列，必須出現(xiàn)在GROUPBY后面。
語(yǔ)法: SELECT "欄位1",SUM("欄位2") FROM "表名" GROUP BY "欄位1";
SELECT Store_Name,SUM(Sales) FROM Store_Info GROUP BY Store_Name ORDER BY sales desc;
------- HAVING ----用來(lái)過(guò)濾由 GROUP BY 語(yǔ)句返回的記錄集，通常與 GROUP BY 語(yǔ)句聯(lián)合使用
HAVING 語(yǔ)句的存在彌補(bǔ)了 WHERE 關(guān)鍵字不能與聚合函數(shù)聯(lián)合使用的不足。如果被 SELECT 的只有函數(shù)欄，那就不需要GROUP BY子句。
語(yǔ)法: SELECT "欄位1",SUM("欄位2") FROM "表名" GROUP BY "欄位1" HAVING (函數(shù)條件);
SELECT Store_Name,SUM(Sales) FROM Store_Info GROUP BY Store_Name HAVING SUM(Sales) > 1500;
---- ----別名---------欄位別名 表格別名
語(yǔ)法: SELECT "表格別名"."欄位1" [AS] "欄位別名" FROM "表格名" [AS] "表格別名";
SELECT A.Store_Name Store,SUM(A.Sales) "Total Sales" FROM Store_Info A GROUP BY A.Store_Name;
---------子查詢(xún)--------連接表格，在WHERE子句或HAVING 子句中插入另一個(gè)SQL語(yǔ)句
語(yǔ)法: SELECT "欄位1" FROM "表格1" WHERE "欄位2” [比較運(yùn)算符] #外查詢(xún)
(SELECT "欄位1" FROM "表格2" WHERE "條件"); #內(nèi)查詢(xún)
#可以是符號(hào)的運(yùn)算符，例如=、>、=、<= ;也可以是文字的運(yùn)算符，例如 LIKE、IN、BETWEEN
SELECT SUM(Sales) FROM Store_Info WHERE Store_Name IN
(SELECT Store_Name FROM location WHERE Region = 'West');
SELECT SUM(A.Sales) FROM Store_Info A WHERE A.Store_Name IN
(SELECT Store_Name FROM location B WHERE B.Store_Name = A.Store_Name);
SELECT Store_Name,SUM(Sales),COUNT(Sales) FROM Store_Info GROUP BY Store_Name ORDER BY Sales;
+-------------+------------+--------------+
| Store_Name | SUM(Sales) | COUNT(Sales) |
+-------------+------------+--------------+
| Houston | 250 | 1 |
| Boston | 700 | 1 |
| Los Angeles | 1800 | 2 |
+-------------+------------+--------------+
3 rows in set (0.01 sec)
------- EXISTS ------用來(lái)測(cè)試內(nèi)查詢(xún)有沒(méi)有產(chǎn)生任何結(jié)果，類(lèi)似布爾值是否為真
#如果有的話(huà)，系統(tǒng)就會(huì)執(zhí)行外查詢(xún)中的SQL語(yǔ)句。若是沒(méi)有的話(huà)，那整個(gè)SQL語(yǔ)句就不會(huì)產(chǎn)生任何結(jié)果。
語(yǔ)法: SELECT "欄位1" FROM "表格1" WHERE EXISTS (SELECT * FROM "表格2" WHERE "條件");
SELECT SUM(Sales) FROM Store_Info WHERE EXISTS (SELECT * FROM location WHERE Region = 'West');
SELECT SUM(Sales) FROM Store_Info WHERE Store_Name IN ('Los Angeles','Houston');
+------------+
| SUM(Sales) |
+------------+
| 2050 |
+------------+
1 row in set (0.00 sec)
--------------連接查詢(xún)----------------
location 表格如下:
+--------+-------------+
| Region | Store_Name |
+--------+-------------+
| East | Boston |
| East | New York |
| West | Los Angeles |
| West | Houston |
+--------+-------------+
4 rows in set (0.00 sec)
UPDATE Store_Info SET store_name='Washington' WHERE sales=300;
Store_Info 表格如下：
mysql> select * from Store_Info;
+-------------+-------+------------+
| Store_Name | Sales | Date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Houston | 250 | 2020-12-07 |
| Washington | 300 | 2020-12-08 |
| Boston | 700 | 2020-12-08 |
+-------------+-------+------------+
4 rows in set (0.00 sec)
inner join(等值相連): 只返回兩個(gè)表中聯(lián)結(jié)字段相等的行
left join(左聯(lián)接): 返回包括左表中的所有記錄和右表中聯(lián)結(jié)字段相等的記錄
right join(右聯(lián)接): 返回包括右表中的所有記錄和左表中聯(lián)結(jié)字段相等的記錄
SELECT * FROM location A INNER JOIN Store_Info B on A.Store_Name = B.Store_Name;
SELECT * FROM location A RIGHT JOIN Store_Info B on A.Store_Name = B.Store_Name;
SELECT * FROM location A,Store_Info B WHERE A.Store_Name = B.Store_Name;
SELECT A.Region REGION,SUM(B.Sales) SALES FROM location A,Store_Info B WHERE A.Store_Name = B.Store_Name GROUP BY REGION;
-------------CREATE VIEW---------視圖，可以被當(dāng)作是虛擬表或存儲(chǔ)查詢(xún)
視圖跟表格的不同是，表格中有實(shí)際儲(chǔ)存資料，而視圖是建立在表格之上的一個(gè)架構(gòu)，它本身并不實(shí)際儲(chǔ)存資料。
臨時(shí)表在用戶(hù)退出或同數(shù)據(jù)庫(kù)的連接斷開(kāi)后就自動(dòng)消失了，而視圖不會(huì)消失。
視圖不含有數(shù)據(jù)，只存儲(chǔ)它的定義，它的用途一般可以簡(jiǎn)化復(fù)雜的查詢(xún)。比如你要對(duì)幾個(gè)表進(jìn)行連接查詢(xún)，而且還要進(jìn)行統(tǒng)計(jì)排序等操作，寫(xiě)的SQL語(yǔ)句會(huì)很麻煩的，用視圖將幾個(gè)表聯(lián)結(jié)起來(lái)，然后對(duì)這個(gè)視圖進(jìn)行查詢(xún)操作，就和對(duì)一個(gè)表查詢(xún)一樣，很方便。
語(yǔ)法: CREATE VIEW "視圖表名" AS "SELECT 語(yǔ)句";
CREATE VIEW V_REGION_SALES AS SELECT A.Region REGION,SUM(B.Sales) SALES FROM location A INNER JOIN Store_Info B ON A.Store_Name = B.Store_Name GROUP BY REGION;
SELECT * FROM V_REGION_SALES;
DROP VIEW V_REGION_SALES; #刪除視圖
------------UNION-------聯(lián)集，將兩個(gè)SQL語(yǔ)句的結(jié)果合并起來(lái)，兩個(gè)SQL語(yǔ)句所產(chǎn)生的欄位需要是同樣的資料種類(lèi)
UNION: 生成結(jié)果的資料值將沒(méi)有重復(fù)，且按照字段的順序進(jìn)行排序
語(yǔ)法: [SELECT 語(yǔ)句1] UNION [SELECT 語(yǔ)句2];
UNION ALL: 將生成結(jié)果的資料值都列出來(lái)，無(wú)論有無(wú)重復(fù)
語(yǔ)法: [SELECT 語(yǔ)句1] UNION ALL [SELECT 語(yǔ)句2];
SELECT Store_Name FROM location UNION SELECT Store_Name FROM Store_Info;
SELECT Store_Name FROM location UNION ALL SELECT Store_Name FROM Store_Info;
-------------交集值------- 取兩個(gè)SQL語(yǔ)句結(jié)果的交集
SELECT A.Store_Name FROM location A INNER JOIN Store_Info B ON A.Store_Name = B.Store_Name;
SELECT A.Store_Name FROM location A INNER JOIN Store_Info B USING(Store_Name);
SELECT A.Store_Name FROM
(SELECT Store_Name FROM location UNION ALL SELECT Store_Name FROM Store_Info) A
GROUP BY A.Store_Name HAVING COUNT(*) > 1;
#取兩個(gè)SQL語(yǔ)句結(jié)果的交集，且沒(méi)有重復(fù)
SELECT A.Store_Name FROM (SELECT A.Store_Name FROM location A INNER JOIN Store_Info B ON A.Store_Name = B.Store_Name) A
GROUP BY A.Store_Name HAVING COUNT(*) >= 1;
SELECT DISTINCT A.Store_Name FROM location A INNER JOIN Store_Info B USING(Store_Name); _Name);
--------------無(wú)交集值-------顯示第一個(gè)SQL語(yǔ)句的結(jié)果，且與第二個(gè)SQL語(yǔ)句沒(méi)有交集的結(jié)果，且沒(méi)有重復(fù)
SELECT DISTINCT Store_Name FROM location WHERE (Store_Name) NOT IN (SELECT Store_Name FROM Store_Info);
SELECT DISTINCT A.Store_Name FROM location A
LEFT JOIN Store_Info B USING(Store_Name) WHERE B.Store_Name IS NULL;
----------- CASE --------是SQL用來(lái)做為 IF-THEN-ELSE 之類(lèi)邏輯的關(guān)鍵字
語(yǔ)法:
SELECT CASE ("欄位名")
WHEN "條件1" THEN "結(jié)果1"
WHEN "條件2" THEN "結(jié)果2"
......
[ELSE "結(jié)果N"]
END
FROM "表名";
#"條件"可以是一個(gè)數(shù)值或是公式。ELSE 子句則并不是必須的。
SELECT Store_Name，CASE Store_Name
WHEN 'Los Angeles' THEN Sales * 2
WHEN 'Boston' THEN Sales * 1.5
ELSE Sales
END
"New Sales", Date
FROM Store_Info;
#"New sales" 是用于 CASE 那個(gè)欄位的欄位名
#創(chuàng)建一個(gè)新表：
CREATE TABLE Total_Sales (Name char(10),Sales int(5));
INSERT INTO Total_Sales VALUES ('zhangsan',10);
INSERT INTO Total_Sales VALUES ('lisi',15);
INSERT INTO Total_Sales VALUES ('wangwu',20);
INSERT INTO Total_Sales VALUES ('zhaoliu',40);
INSERT INTO Total_Sales VALUES ('sunqi',50);
INSERT INTO Total_Sales VALUES ('zhouba',20);
INSERT INTO Total_Sales VALUES ('wujiu',30);
Total_Sales 表格如下:
mysql> select * from Total_Sales;
+----------+-------+
| Name | Sales |
+----------+-------+
| zhangsan | 10 |
| lisi | 15 |
| wangwu | 20 |
| zhaoliu | 40 |
| sunqi | 50 |
| zhouba | 20 |
| wujiu | 30 |
+----------+-------+
7 rows in set (0.00 sec)
-------算排名 ------表格自我連結(jié) (self Join)，然后將結(jié)果依序列出，算出每一行之前(包含那一行本身)有多少行數(shù)
SELECT A1.Name,A1.Sales,COUNT(A2.Sales) Rank FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;
#統(tǒng)計(jì)sales欄位的值是比自已本身的值小的以及sales欄位和Name欄位都相同的數(shù)量，比如zhangsan為5+1=6
----------算中位數(shù) ------------
SELECT Sales Middle FROM (SELECT A1.Name,A1.Sales,COUNT(A2.Sales) Rank FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name <= A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC) A3
WHERE A3.Rank = (SELECT (COUNT(*)+1) DIV 2 FROM Total_Sales);
#每個(gè)派生表必須有自己的別名，所以別名 A3 必須要有
#DIV 是在MySQL中算出商的方式
-------- 算累積總計(jì)-------表格自我連結(jié)(Self Join)， 然后將結(jié)果依序列出，算出每一行之前(包含那一行本身)的總合
SELECT A1.Name,A1.Sales,SUM(A2.Sales) Sum_Total FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;
---------算總合百分比--------------
SELECT A1.Name,A1.Sales,A1.Sales/(SELECT SUM(Sales) FROM Total_Sales) Per_Total
FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;
#SELECT SUM(Sales) FROM Total_sales 這一段子查詢(xún)是用來(lái)算出總合
#總合算出后，我們就能夠?qū)⒚恳恍幸灰怀钥偤蟻?lái)求出每一行的總合百分比
--------算累積總合百分比--------------
SELECT A1.Name,A1.Sales,SUM(A2.Sales)/(SELECT SUM(Sales) FROM Total_Sales) Per_Total
FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales and A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;
#用累積總計(jì)SUM(a2.sales) 除以總合來(lái)求出每一行的累積總合百分比.
SELECT A1.Name,A1.sales,TRUNCATE(ROUND(SUM(A2.Sales)/(SELECT SUM(Sales) FROM Total_Sales),4)*100,2) || '%' Per_Total
FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales and A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;
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