How to use a foreign key in sqlite?

问题

I have two tables in sqlite, which are "connected" with an id. The app using this tables is running on Android OS.

Table 1;:

|id| entry 1| entry2|
|1 | aaaaaa | aaaaa |
|2 | bbbbbb | bbbbb |

Table 2:

|id| entryx| constant|
|1 | aaaaa | aaaaaaaa|
|1 | baaaa | baaaaaaa|
|1 | caaaa | caaaaaaa|
|2 | ababa | baabaaba|

At the moment I delete entries with the following query, by using a loop:

do{
    db.delete("Table 1","id='"+cid+"'",null);
    db.delete("Table 2","id='"+cid+"'",null);
  }
while(getNextID());

I want to use a foreign key, which allows me to delete the entry in table 1 and all entries in table 2 are deleted as well. Besides, I have to consider that the data in table 1 are inserted, before they are inserted in table 2. How can I use a foreign key to do this? The table is using id as int and it is the primary key, the same is used for the second table.

回答1:

As selvin suggested use on delete cascade

http://www.sqlite.org/foreignkeys.html

Table1

CREATE TABLE table1 (
  id PRIMARY KEY  
 ,entry1 text,entry2 text
);

Then

insert into table1 values(1,"aaaa","aaaaa");
insert into table1 values(2,"bbbb","bbbbb");

Table2

CREATE TABLE table2(
  id int references table1(id) ON DELETE CASCADE, entryx text, constant text
);


insert into table2 values(1,"aaaa","aaaaa");
insert into table2 values(1," baaaa ","baaaaaaa");
insert into table2 values(1,"  caaaa ","caaaaaaa")
insert into table2 values(2,"bbbb","bbbbb");

Tables after entry

sqlite> select * from table1;
id          entry1      entry2    
----------  ----------  ----------
1           aaaa        aaaaa     
2           bbbb        bbbbb     
sqlite> select * from table2;
id          entryx      constant  
----------  ----------  ----------
1           aaaa        aaaaa      
1           baaaa       baaaaaaa  
1           caaaa       caaaaaaa  
2           bbbb        bbbbb

Delete

sqlite> delete from table1 where id=1;

Tables after delete

sqlite> select * from table2;
id          entryx      constant  
----------  ----------  ----------
2           bbbb        bbbbb     


sqlite> select * from table1;
id          entry1      entry2    
----------  ----------  ----------
2           bbbb        bbbbb

来源：https://stackoverflow.com/questions/21312276/how-to-use-a-foreign-key-in-sqlite

标签

android

sqlite

foreign-keys

android-sqlite