Mysql查询选择具有不同列值的结果

Question

I have a table that displays books. However I would like only only 1 book to be shown per unique email address ( strContactEmail ). I tried the below query, it didn't work. Any help greatly appreciated.`

$sql =  "SELECT lngbookid, strTitle, strAuthor, strcoursecode, strISBN, ".
        " strcontactname, DISTINCT(strContactEmail) AS strContactEmail, ".
        " curPrice, ysnsalerent, dtmpostdate, memcomments, school, ".
        " ASIN, BookIMG, ISBN10, ISBN13, Updated, ".
        " datetime, user_ip, NoOtherBooks ".
        " FROM tblbooks ".
        " WHERE strcoursecode LIKE '%$search%'  ".
        " ORDER BY datetime DESC LIMIT 50";

Answer 1

Try a GROUP BY statement:

http://www.w3schools.com/sql/sql_groupby.asp

Answer 2

The easiest way:

 
 
 
 
  
  
  SELECT max(lngbookid) as lngbookid, max(strtitle) as strtitle, max(strauthor) as strauthor, max(strcoursecode) as strcoursecode, max(strisbn) as strisbn, max(strcontactname) as strcontactname, strcontactemail, max(curprice) as curprice, max(ysnsalerent) as ysnsalerent, max(dtmpostdate) as dtmpostdate, max(memcomments) as memcomments, max(school) as school, max(asin) as asin, max(bookimg) as bookimg, max(isbn10) as isbn10, max(isbn13) as isbn13, max(updated) as updated, max(datetime) as datetime, max(user_ip) as user_ip, max(nootherbooks) as nootherbooks FROM tblbooks WHERE strcoursecode LIKE '%$search%' GROUP BY strcontactemail ORDER BY datetime DESC LIMIT 50
 
 
  

EDIT Well, the above was actually too "dummy". Better way to do this is (providing that column "lngbookid" is a primary key):

SELECT a.lngbookid,
       a.strtitle,
       a.strauthor,
       a.strcoursecode,
       a.strisbn,
       a.strcontactname,
       a.strcontactemail,
       a.ontactemail,
       a.curprice,
       a.ysnsalerent,
       a.dtmpostdate,
       a.memcomments,
       a.school,
       a.asin,
       a.bookimg,
       a.isbn10,
       a.isbn13,
       a.updated,
       a.datetime,
       a.user_ip,
       a.nootherbooks
FROM   tblbooks AS a
       JOIN (SELECT strcontactemail,
                    Max(lngbookid) AS lngbookid
             FROM   tblbooks
             GROUP  BY strcontactemail) AS b
         ON ( a.strcontactemail = b.strcontactemail
              AND a.lngbookid = b.lngbookid )