mySQL >> Adding HREF links to a Distinct GROUP_CONCAT

问题

I have the following query:

SELECT *, RES.res_id 'ID', RES.RES_Title 'Title', 
GROUP_CONCAT(DISTINCT T.T_Name separator ', ') 'Topics', 
GROUP_CONCAT(DISTINCT CH.CH_Code separator ', ') 'Chapters' 
FROM Resources RES 
LEFT JOIN topic_to_resource RT ON RT.RT_ResourceID = RES.RES_ID 
LEFT JOIN topics T on T.T_ID = RT.RT_TopicID 
LEFT JOIN topic_to_chapter TCH on TCH.TCH_TopicID = T.T_ID 
LEFT JOIN chapters CH ON CH.CH_ID = TCH.TCH_FrameworkID 
WHERE RES_Status = 'Active' 
GROUP BY RES.RES_ID 
ORDER BY RES_Title ASC, RES_Source DESC LIMIT 0, 10

For each of the GROUP_CONCATs (Topics and Chapters), I need to convert the list into links while keeping the Distinct.

For example, instead of the Topics output of the query above: Sports, Current Events, Politics, Climate, etc.

I need to generate:

<a href="page.asp?topic=Sports" title="Sports">Sports</a>, 
<a href="page.asp?topic=Current%20Events" title="Current Events">Current Events</a>, 
<a href="page.asp?topic=Politics" title="Politics">Politics</a>, 
<a href="page.asp?topic=Climate" title="Climate">Climate</a>

I can achieve the links by nesting a CONCAT within the GROUP_CONCAT, but then I lose the Distinct. Also, I need the query to stay grouped by the Resource ID (RES.RES_ID).

Any ideas on how to accomplish a linked list of distinct topics and chapters?

Many thanks in advance!

回答1:

Following on from this question, and using that query as the basis for the following example, you can do this with the following:

SELECT 
CONCAT(res_id,': ',res_name) 'Resources', 
GROUP_CONCAT(distinct t_name order by t_id separator ',') 'Topics', 
GROUP_CONCAT(distinct ch_name order by ch_id separator ',') 'Chapters'
FROM (SELECT res_id,
      res_name,
      t_id,
      t_name,
      ch_id, 
      CONCAT("<a href=\"page.asp?topic=",ch_name,"\" title=\"",ch_name,"\">",ch_name,"</a>") as ch_name 
             FROM resources r
             JOIN topics_to_resource ttr ON ttr.tr_resid = r.res_id
             JOIN topics t on t.t_id = ttr.tr_tid
             JOIN topics_to_chapter ttc on ttc.tch_tid = t.t_id
             JOIN chapters ch ON ch.ch_id = tch_chid) links
      GROUP BY res_id
      ORDER BY res_id, t_id, ch_id;

Basically I have wrapped the source data in a separate (sub) query, building the links, then performing the GROUP_CONCATs outside of this.

This produces:

<a href="page.asp?topic=CHAPTER #1" title="CHAPTER #1">CHAPTER #1</a>,
<a href="page.asp?topic=CHAPTER #2" title="CHAPTER #2">CHAPTER #2</a>,
<a href="page.asp?topic=CHAPTER #3" title="CHAPTER #3">CHAPTER #3</a>

See this fiddle for more detail

来源：https://stackoverflow.com/questions/46626600/mysql-adding-href-links-to-a-distinct-group-concat

标签

mysql

distinct

concat

group-concat