建立一个SQL“ toxi”标签系统，如何选择带有特定标签的项目？

Question

First of all, i'm new to sql.

Now, I'm building a tagging system with sqlite for my android app that uses 3 tables (items, tags, tagmap) based on this "toxi" solution found here , but I'm not sure on how the mechanics work, how would I select all items from this itemsTable that have a specific tag.

itemsTable

itemid

2

3

4

tagsTable

tagid tag

2 "ruby"

3 "java"

7 "c"

tagmap

itemid tagid

2 3

3 7

2 2

4 7

I was trying something along the lines of:

SELECT* FROM itemsTable INNER JOIN tagmap ON tagmap.itemid= itemsTable.itemid AND tagmap.tagid=tagsTable.tagid WHERE tagsTable.tagid= desiredid

But this seems to be wrong.

BTW: all itemid and tagsid are primary keys auto-incremented

Any answers or an alternative to creating a tagging system(in which an item can have more than one tag) are welcomed.

Answer 1

Your query is wrong. You did not include the "tagsTable" in your join. Try this:

SELECT* FROM itemsTable INNER JOIN tagmap ON tagmap.itemid= itemsTab 
INNER JOIN tagsTable ON tagmap.tagid=tagsTable.tagid WHERE tagsTable.tagid= desiredID