如何保留外部联接2个表?
class Person {
String firstName
String lastName
String gender
//static hasMany = [votes: Vote]
static mapping = {
version false
}
static constrains = {
}
}
class Vote {
Person voter;
Person subject;
static mapping = {
version false
}
static constraints = {
voter nullable: false
subject nullable: false
}
}
我需要让每个人都不必为特定的人投票。
假设某人1票中有5票中有3票,我需要他没有投票给他的另外2票给他看。
该查询应该如何?
编辑:
def personInstance1 = new Person(firstName: "Antonio", lastName: "Vivaldi", gender: "m")
def personInstance2 = new Person(firstName: "Dennis", lastName: "Rodman", gender: "m")
def personInstance3 = new Person(firstName: "Marc", lastName: "Oh", gender: "m")
def personInstance4 = new Person(firstName: "Gudrun", lastName: "Graublume", gender: "w")
def personInstance5 = new Person(firstName: "Hilde", lastName: "Feuerhorn", gender: "w")
def personInstance6 = new Person(firstName: "Mandy", lastName: "Muller", gender: "w")
personInstance1.save()
personInstance2.save()
personInstance3.save()
personInstance4.save()
personInstance5.save()
personInstance6.save()
def voteInstance1 = new Vote(voter: personInstance1, subject: personInstance2)
def voteInstance2 = new Vote(voter: personInstance1, subject: personInstance3)
def voteInstance3 = new Vote(voter: personInstance1, subject: personInstance4)
def voteInstance4 = new Vote(voter: personInstance1, subject: personInstance5)
def voteInstance5 = new Vote(voter: personInstance2, subject: personInstance1)
voteInstance1.save()
voteInstance2.save()
voteInstance3.save()
voteInstance4.save()
voteInstance5.save()
这是我的文件,Antonio和Dennis已投票,并且每个人都需要提供他们未投票的人的名单。
编辑:
这样一来,我似乎为丹尼斯赢得了成果,因为他只投票了一次,
但是如果我把v.voter_id = 1
为了获得安东尼奥的结果,结果将根据他获得的票数加倍。
SELECT first_name FROM vote as v
LEFT OUTER JOIN person as p
ON v.subject_id != p.id AND v.voter_id = 2
WHERE p.id IS NOT NULL
最佳答案
试试这个:
SELECT * FROM Person P
WHERE NOT EXISTS(
SELECT 'Vote' FROM Vote V
WHERE V.subject = P
)
这样,您将提取所有没有投票的人
编辑
在SQL中,您可以通过以下方式检索矩阵:
CREATE TABLE #person (nome varchar(30))
CREATE TABLE #vote (votante varchar(30), candidato varchar(30))
INSERT INTO #person values
('Antonio Vivaldi'),
('Dennis Rodman'),
('Marc Oh'),
('Gudrun Graublume'),
('Hilde Feuerhorn'),
('Mandy Muller')
INSERT INTO #vote values
('Antonio Vivaldi', 'Dennis Rodman'),
('Antonio Vivaldi', 'Marc Oh'),
('Antonio Vivaldi', 'Gudrun Graublume'),
('Antonio Vivaldi', 'Hilde Feuerhorn'),
('Dennis Rodman', 'Antonio Vivaldi')
SELECT *
FROM #person p
CROSS JOIN #person c
WHERE NOT EXISTS(
SELECT 'X'
FROM #vote v
WHERE v.votante = p.nome
AND v.candidato = c.nome
)
AND p.nome <> c.nome
ORDER BY p.nome
关于grails - grails hql左外连接,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26401377/