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JPQL主要用于JPA查詢(xún)數據，和SQL語(yǔ)句的語(yǔ)法大同小異；

最基本的查詢(xún)：

SELECT p

FROM Player p

查詢(xún)出所有的player,包括其子類(lèi)，也可以寫(xiě)成這樣

From Player as p

去除重復的元素

SELECT DISTINCT

 p

FROM Player p

WHERE p.position = ?1

關(guān)鍵字DISTINCT去除了重復的元素，并且接受參數設置條件過(guò)濾

結合查詢(xún)關(guān)聯(lián)

SELECT DISTINCT p

FROM Player p, IN(p.teams) t

查詢(xún)所有有team的player

也可以寫(xiě)成如下：

SELECT DISTINCT p

FROM Player p JOIN p.teams t

或者：

SELECT DISTINCT p

FROM Player p

WHERE p.team IS NOT EMPTY

關(guān)聯(lián)關(guān)系的查詢(xún)過(guò)濾

SELECT t

 FROM Team tJOIN t.league l

 WHERE l.sport = ’soccer’OR l.sport =’football’

查詢(xún)所有league sports屬性的team對象

SELECT DISTINCT p

FROM Player p, IN (p.teams) t

WHERE t.league.sport = :sport

其他的查詢(xún)表達式

LIKE：

SELECT p

 FROMPlayer p

 WHERE p.name LIKE’Mich%’

IS NULL：

SELECT t

 FROM Team t

 WHEREt.league IS NULL

IS EMPTY：

SELECT p

FROM Player p

WHERE p.teams IS EMPTY

主要用于判斷關(guān)系實(shí)體一對多集合

BETWEEN

SELECT DISTINCT p

FROM Player p

WHERE p.salary BETWEEN :lowerSalary AND:higherSalary

等價(jià)于：

p.salary >= :lowerSalary AND p.salary <=:higherSalary

在判斷日期范圍的時(shí)候尤其有用；

復合條件：

SELECT DISTINCT p1

FROM Player p1, Player p2

WHERE p1.salary > p2.salaryAND p2.name = :name

查找薪水比指定姓名的員工更高的員工

IN：

o.country IN (’UK’, ’US’,’France’)

同時(shí)你也可以在In語(yǔ)句中設置參數：

o.country IN (’UK’, ’US’, ’France’, :country)

子查詢(xún)：

SELECT c

FROM Customer c

WHERE (SELECT COUNT(o) FROM c.orders o) > 10

EXISTS子查詢(xún)：

SELECT DISTINCT emp

FROM Employee emp

WHERE EXISTS (

    SELECTspouseEmp

    FROMEmployee spouseEmp

WHERE spouseEmp = emp.spouse)

ALL和ANY配合=<>=>使用

SELECT emp

FROM Employee emp

WHERE emp.salary > ALL (

    SELECTm.salary

    FROMManager m

    WHEREm.department = emp.department)

其他函數：

算法函數：

返回參數：

1）  實(shí)體對象

SELECT t

FROM Player p, IN (p.teams) t

2) Objecth或者Object[]

SELECT c.name, c.country.name

 FROMcustomer c

 WHERE c.lastname =’Coss’ AND c.firstname = ’Roxane’

返回一個(gè)Object[] list,[0]為name，[1]為country name

Select語(yǔ)句的聚合函數：

如：

SELECT COUNT(l.price)

FROM Order o JOIN o.lineItems lJOIN o.customer c

WHERE c.lastname = ’Incandenza’ AND c.firstname= ’Hal’

構造語(yǔ)句：

SELECT NEWcom.xyz.CustomerDetail(c.name, c.country.name)

 FROMcustomer c

WHERE c.lastname = ’Coss’ ANDc.firstname = ’Roxane’

能夠利用查出的數據直接構造出對象

Order By：

SELECT p.product_name

FROM Order o, IN(o.lineItems) lJOIN o.customer c

WHERE c.lastname = ’Faehmel’ ANDc.firstname = ’Robert’

ORDER BY o.quantity

GROUP BY：

SELECT c.country, COUNT(c)

 FROM Customer c GROUP BYc.country

Having：

SELECT c.status,AVG(o.totalPrice)

 FROM Ordero JOIN o.customer c

GROUP BY c.status HAVING c.statusIN (1, 2, 3)