在sql server中连接表时出现的空值

Question

我想在另一个表格中显示另外一个列数据＆＃34; tbl_link＆＃34;，

SELECT K.KeyWord, 
       kp.KeywordId, 
       kp.CurrentPosition, 
       CONVERT(VARCHAR(2), Psnupdatedate, 106)  shortdate, 
       CONVERT(VARCHAR(12), Psnupdatedate, 106) AS FullDate,
       categoryid 
FROM   seo.Tbl_KeywordPosition kp 
       LEFT JOIN Tbl_ProjAssignment pa 
              ON pa.ProjId = kp.ProjectId 
                 AND pa.KeywordID = kp.keywordId 
     LEFT JOIN Tbl_link l 
              ON l.KeywordID = kp.keywordId 
     LEFT JOIN Tbl_keywords k 
              ON k.KeywordID = kp.keywordId 
WHERE  ProjectId = '109' 
       AND pa.username = 'gangabhavani' 
       AND kp.KeywordID = '1467' 
       AND CONVERT(CHAR(4), PsnUpdateDate, 100) = 'Jan' 
       AND CONVERT(CHAR(4), PsnUpdateDate, 112) = '2015' 
ORDER  BY KeyWord, 
          FullDate ASC 

当前输出：

keyword           keywordid  keywordposition shortdate FULLDATE   categoryid
homeopathy clinics    1467      16  21           21 Jan 2015   NULL
homeopathy clinics    1467      8   22           22 Jan 2015   NULL
homeopathy clinics    1467      11  23           23 Jan 2015   NULL

预期结果

keyword                      keywordid  keywordposition shortdate   FullDate CategoryId
homeopathy clinics in Hyderabad 1467    16           21   21 Jan 2015      ?
homeopathy clinics in Hyderabad 1467    8            22   22 Jan 2015      ?
homeopathy clinics in Hyderabad 1467    11           23   23 Jan 2015      ?

如何制作加入和展示类别

category表包含这些列

LinkId | LinkName | CategoryId | KeywordID | ProjectId

如果我将1=1加入tbl_link加入所有活动？