How to implement tag counting

Question

I have my tags desinged like this in my database:

Table: Item 
Columns: ItemID, Title, Content 

Table: Tag 
Columns: TagID, Title 

Table: ItemTag 
Columns: ItemID, TagID



//example -- this is the right sidebar of stackoverflow
c# × 59279
sql × 14885
asp.net-mvc × 9123
linq × 4337
tags × 339

if I wanted to know the count of each tag such as how stackoverflow counts their tags how would I do it? What kind of query would I perform. I am open to both regular sql and linq

Answer 1

在表标签中添加另一列作为计数器。当您从项目中添加或删除标签时，您会更新计数器（换句话说，当在 Itemtag 上添加行时，标签表上的计数器会增加，当删除时，计数器会减少）

为项目添加标签：

INSERT INTO Itemtag (itemid,tagid) VALUES ('$itemid','$tagid');
UPDATE Tag SET counter=counter+1 WHERE tagid='$tagid';

从项目中删除标签

DELETE FROM Itemtag WHERE itemid='$itemid' AND tagid='$tagid';
UPDATE Tag SET counter=counter-1 WHERE tagid='$tagid';

使用计数器检索项目标签

SELECT t.title, t.counter FROM Itemtag AS it JOIN Tag AS t ON t.idtag=it.tagid 
WHERE it.itemid='$itemid'