[英]many-to-many relationship,, querying one side depending on its elements
Here is the most relevant part of my database schema: 这是我的数据库架构中最相关的部分:
create table TEST (
ID integer not null,
NAME text not null,
constraint PK_TEST primary key (ID),
constraint UNQ_TEST_NAME unique (NAME)
);
create table SESSION (
ID integer not null,
constraint PK_SESSION primary key (ID)
);
create table SESSION_TEST (
SESSION_ID integer not null,
TEST_ID integer not null,
ORDINAL integer not null,
constraint PK_SESSION_TEST primary key (SESSION_ID, TEST_ID),
constraint FK_SESSION_TEST_SESSION_ID foreign key (SESSION_ID) references SESSION (ID) on delete cascade,
constraint FK_SESSION_TEST_TEST_ID foreign key (TEST_ID) references TEST (ID) on delete cascade,
constraint UNQ_SESSION_TEST_SESSION_ID_ORDINAL unique (SESSION_ID, ORDINAL)
);
There are SESSIONS that consist of multiple TESTS. 有些会话包含多个TESTS。 TESTs in SESSIONS have ORDINALs (are ordered).
SESSIONS中的TEST具有ORDINAL(已订购)。 SESSION_TEST is a link table for a many-to-many relationship: one test can be a part of multiple sessions, and one session consists of multiple tests (but one test can be in a session only once, which is the PK).
SESSION_TEST是用于多对多关系的链接表:一个测试可以是多个会话的一部分,一个会话可以包含多个测试(但是一个测试只能在一个会话中出现一次,即PK)。
I am having problems writing an SQL statement that would return true (or 1 actually, as I am using SQLite) for a test with a given ID, if there is a session that has that test and only that test (in other words, the session consists of only one test, the one I am looking for). 如果存在具有该测试且仅该测试的会话(换句话说,会话仅包含一项测试,我正在寻找一种测试)。 For example:
例如:
TEST:
ID|NAME
1|aaa
2|bbb
3|ccc
SESSION:
ID
1
2
3
4
SESSION_TEST:
SESSION_ID|TEST_ID|ORDINAL
1|1|1
1|2|2
2|1|1
3|3|1
SESSION with ID = 1 has two TESTs, and SESSIONs 2 and 3 have one test each. ID = 1的SESSION具有两个TEST,SESSION 2和3分别具有一个测试。 I would need to have a select that would return 1/true for inputs 1 and 3, but 0 for 2 (as this TEST is only in SESSION 1, but it's not the only one).
我需要一个选择,对于输入1和输入3将返回1 / true,但对于输入2将返回0(因为此TEST仅在SESSION 1中,但不是唯一的)。
(Sorry about the title, I really didn't know how to put it in a few sentences and make it clear!). (对不起标题,我真的不知道如何用几句话把它弄清楚!)。
RETURN EXISTS SELECT SESSION_ID FROM
SESSION_TEST
WHERE TEST_ID = @id
AND ORDINAL = 1
AND SESSION_ID NOT IN (SELECT SESSION_ID FROM SESSION_TEST WHERE ORDINAL > 1);
The RETURN EXISTS
syntax might be TSQL only, but you get the picture. RETURN EXISTS
语法可能仅是TSQL,但是您可以理解。 If the query returns rows, return true, if not return false. 如果查询返回行,则返回true,否则返回false。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.