SQL進階之關聯子查詢
一、關聯子查詢簡介
通過關聯表內部條件從而達到查詢效果
二、關聯子查詢實操
注:版本使用:mysql5.1.73
以下代碼均可直接cv在mysql練習
1.CreateTable
--移動累計值和移動平均值
CREATE TABLE Accounts
(prc_date DATE NOT NULL ,
prc_amt INTEGER NOT NULL ,
PRIMARY KEY (prc_date)) ;
INSERT INTO Accounts VALUES ('2006-10-26', 12000 );
INSERT INTO Accounts VALUES ('2006-10-28', 2500 );
INSERT INTO Accounts VALUES ('2006-10-31', -15000 );
INSERT INTO Accounts VALUES ('2006-11-03', 34000 );
INSERT INTO Accounts VALUES ('2006-11-04', -5000 );
INSERT INTO Accounts VALUES ('2006-11-06', 7200 );
INSERT INTO Accounts VALUES ('2006-11-11', 11000 );
--查詢重疊的時間區間
CREATE TABLE Reservations
(reserver VARCHAR(30) PRIMARY KEY,
start_date DATE NOT NULL,
end_date DATE NOT NULL);
INSERT INTO Reservations VALUES('木村', '2006-10-26', '2006-10-27');
INSERT INTO Reservations VALUES('荒木', '2006-10-28', '2006-10-31');
INSERT INTO Reservations VALUES('堀', '2006-10-31', '2006-11-01');
INSERT INTO Reservations VALUES('山本', '2006-11-03', '2006-11-04');
INSERT INTO Reservations VALUES('內田', '2006-11-03', '2006-11-05');
INSERT INTO Reservations VALUES('水谷', '2006-11-06', '2006-11-06');
--山本的入住日期爲4日時
DELETE FROM Reservations WHERE reserver = '山本';
INSERT INTO Reservations VALUES('山本', '2006-11-04', '2006-11-04');
--增長、減少、維持現狀
CREATE TABLE Sales
(year INTEGER NOT NULL ,
sale INTEGER NOT NULL ,
PRIMARY KEY (year));
INSERT INTO Sales VALUES (1990, 50);
INSERT INTO Sales VALUES (1991, 51);
INSERT INTO Sales VALUES (1992, 52);
INSERT INTO Sales VALUES (1993, 52);
INSERT INTO Sales VALUES (1994, 50);
INSERT INTO Sales VALUES (1995, 50);
INSERT INTO Sales VALUES (1996, 49);
INSERT INTO Sales VALUES (1997, 55);
--時間軸有間斷時：和過去最臨近的時間進行比較
CREATE TABLE Sales2
(year INTEGER NOT NULL ,
sale INTEGER NOT NULL ,
PRIMARY KEY (year));
INSERT INTO Sales2 VALUES (1990, 50);
INSERT INTO Sales2 VALUES (1992, 50);
INSERT INTO Sales2 VALUES (1993, 52);
INSERT INTO Sales2 VALUES (1994, 55);
INSERT INTO Sales2 VALUES (1997, 55);
2.Sample
/* 求與上一年營業額一樣的年份（1）：使用關聯子查詢 */
SELECT YEAR,sale
FROM Sales S1
WHERE sale = (SELECT sale
FROM Sales S2
WHERE S2.year = S1.year - 1)
ORDER BY YEAR;
/* 求與上一年營業額一樣的年份（2）：使用自連接 */
SELECT S1.year, S1.sale
FROM Sales S1,
Sales S2
WHERE S2.sale = S1.sale
AND S2.year = S1.year - 1
ORDER BY YEAR;
/* 求出是增長了還是減少了，抑或是維持現狀（1）：使用關聯子查詢 */
SELECT S1.year, S1.sale,
CASE WHEN sale =
(SELECT sale
FROM Sales S2
WHERE S2.year = S1.year - 1) THEN '→' /* 持平 */
WHEN sale >
(SELECT sale
FROM Sales S2
WHERE S2.year = S1.year - 1) THEN '↑' /* 增長 */
WHEN sale <
(SELECT sale
FROM Sales S2
WHERE S2.year = S1.year - 1) THEN '↓' /* 減少 */
ELSE '—' END AS var
FROM Sales S1
ORDER BY YEAR;
/* 求出是增長了還是減少了，抑或是維持現狀（2）：使用自連接查詢 */
SELECT S1.year, S1.sale,
CASE WHEN S1.sale = S2.sale THEN '→'
WHEN S1.sale > S2.sale THEN '↑'
WHEN S1.sale < S2.sale THEN '↓'
ELSE '—' END AS var
FROM Sales S1, Sales S2
WHERE S2.year = S1.year-1
ORDER BY YEAR;
/* 查詢與過去最臨近的年份營業額相同的年份 */
SELECT YEAR, sale
FROM Sales2 S1
WHERE sale =
(SELECT sale
FROM Sales2 S2
WHERE S2.year =
(SELECT MAX(YEAR) /* 條件2：在滿足條件1的年份中，年份最早的一個 */
FROM Sales2 S3
WHERE S1.year > S3.year)) /* 條件1：與該年份相比是過去的年份 */
ORDER BY YEAR;
/* 查詢與過去最臨近的年份營業額相同的年份：同時使用自連接 */
SELECT S1.year AS YEAR,
S1.sale AS sale
FROM Sales2 S1, Sales2 S2
WHERE S1.sale = S2.sale
AND S2.year = (SELECT MAX(YEAR)
FROM Sales2 S3
WHERE S1.year > S3.year)
/* 求每一年與過去最臨近的年份之間的營業額之差（1）：結果裏不包含最早的年份 */
SELECT S2.year AS pre_year,
S1.year AS now_year,
S2.sale AS pre_sale,
S1.sale AS now_sale,
S1.sale - S2.sale AS diff
FROM Sales2 S1, Sales2 S2
WHERE S2.year = (SELECT MAX(year)
FROM Sales2 S3
WHERE S1.year > S3.year)
ORDER BY now_year;
/* 求每一年與過去最臨近的年份之間的營業額之差（2）：使用自外連接。結果裏包含最早的年份 */
SELECT S2.year AS pre_year,
S1.year AS now_year,
S2.sale AS pre_sale,
S1.sale AS now_sale,
S1.sale - S2.sale AS diff
FROM Sales2 S1 LEFT OUTER JOIN Sales2 S2
ON S2.year = (SELECT MAX(year)
FROM Sales2 S3
WHERE S1.year > S3.year)
ORDER BY now_year;
/* 求累計值：使用窗口函數 */(mysql不支持窗口函數,hivesql可以用)
SELECT prc_date, prc_amt,
SUM(prc_amt) OVER (ORDER BY prc_date) AS onhand_amt
FROM Accounts;
/* 求累計值：使用馮·諾依曼型遞歸集合 */
SELECT prc_date, A1.prc_amt,
(SELECT SUM(prc_amt)
FROM Accounts A2
WHERE A1.prc_date >= A2.prc_date ) AS onhand_amt
FROM Accounts A1
ORDER BY prc_date;
/* 求移動累計值（1）：使用窗口函數 */(hivesql使用,mysql不支持)
SELECT prc_date, prc_amt,
SUM(prc_amt) OVER (ORDER BY prc_date
ROWS 2 PRECEDING) AS onhand_amt
FROM Accounts;
/* 求移動累計值（2）：不滿3行的時間區間也輸出 */
SELECT prc_date, A1.prc_amt,
(SELECT SUM(prc_amt)
FROM Accounts A2
WHERE A1.prc_date >= A2.prc_date
AND (SELECT COUNT(*)
FROM Accounts A3
WHERE A3.prc_date
BETWEEN A2.prc_date AND A1.prc_date ) <= 3 ) AS mvg_sum
FROM Accounts A1
ORDER BY prc_date;
/* 求移動累計值（3）：不滿3行的區間按無效處理 */
SELECT prc_date, A1.prc_amt,
(SELECT SUM(prc_amt)
FROM Accounts A2
WHERE A1.prc_date >= A2.prc_date
AND (SELECT COUNT(*)
FROM Accounts A3
WHERE A3.prc_date
BETWEEN A2.prc_date AND A1.prc_date ) <= 3
HAVING COUNT(*) =3) AS mvg_sum /* 不滿3行數據的不顯示 */
FROM Accounts A1
ORDER BY prc_date;
/* 求重疊的住宿期間 */
SELECT reserver, start_date, end_date
FROM Reservations R1
WHERE EXISTS
(SELECT *
FROM Reservations R2
WHERE R1.reserver <> R2.reserver /* 與自己以外的客人進行比較 */
AND ( R1.start_date BETWEEN R2.start_date AND R2.end_date /* 條件（1）：自己的入住日期在他人的住宿期間內 */
OR R1.end_date BETWEEN R2.start_date AND R2.end_date)); /* 條件（2）：自己的離店日期在他人的住宿期間內 */
/* 升級版：把完全包含別人的住宿期間的情況也輸出 */
SELECT reserver, start_date, end_date
FROM Reservations R1
WHERE EXISTS
(SELECT *
FROM Reservations R2
WHERE R1.reserver <> R2.reserver
AND ( ( R1.start_date BETWEEN R2.start_date AND R2.end_date
OR R1.end_date BETWEEN R2.start_date AND R2.end_date)
OR ( R2.start_date BETWEEN R1.start_date AND R1.end_date
AND R2.end_date BETWEEN R1.start_date AND R1.end_date)));
/* 簡化多行數據的比較*/
SELECT S1.year, S1.sale,
CASE SIGN(sale -
(SELECT sale
FROM Sales S2
WHERE S2.year = S1.year - 1) )
WHEN 0 THEN '→' /* 持平 */
WHEN 1 THEN '↑' /* 增長 */
WHEN -1 THEN '↓' /* 減少 */
ELSE '—' END AS var
FROM Sales S1
ORDER BY YEAR;
參考資料:《SQL進階教程》| MICK