我使用连接和联合的 SQL 查询有什么问题？

Question

What's wrong with my sql query? I am trying to use a Join and at the same time a UNION to get all table from another table while joining other tables together based on a relationship ..

However I get the following error:

"The used SELECT statements have a different number of columns"

My query:

SELECT a.ESN, a.UnixTime, a.Payload, a.Timestamp
                ,b.AlarmingStatus
                ,b.STxModel
                ,c.GroupID
                FROM STxMessage a
                JOIN STx b ON b.ESN = a.ESN
                JOIN GroupInfo c ON b.GroupID = c.GroupID
                WHERE b.STxModel = 190
                AND a.AlarmsChecked="y"
                AND c.AlertsMasterSwitch="on"
               UNION ALL 
      SELECT d.ESN , d.UnixTime,  d.Payload,  d.Timestamp FROM STxMessageArchive d

Answer 1

The error message says it all.

When using UNION , the columns return by the combined SELECT statement must be the same, eg.

SELECT col1, col2, col3 FROM table1
UNION
SELECT col1, col2, col3 FROM table2

if the columns do not match, you can still combine it provided that you have to provide dummy data for the column, eg

SELECT col1, col2, col3 FROM table1
UNION
SELECT col1, col2, '' AS col3 FROM table2

so in your query, it should look like this

SELECT  a.ESN, a.UnixTime, a.Payload, a.Timestamp ,
        b.AlarmingStatus, b.STxModel, c.GroupID
FROM    STxMessage a
        INNER JOIN STx b 
            ON b.ESN = a.ESN
        INNER JOIN GroupInfo c 
            ON b.GroupID = c.GroupID
WHERE   b.STxModel = 190 AND 
        a.AlarmsChecked="y" AND 
        c.AlertsMasterSwitch="on"
UNION ALL 
SELECT  d.ESN, d.UnixTime, d.Payload, d.Timestamp,
        NULL AS AlarmingStatus, NULL AS STxModel, NULL AS GroupID
FROM    STxMessageArchive d

Answer 2

hi this are the extra columns in your first query

 ,b.AlarmingStatus
 ,b.STxModel
 ,c.GroupID

you need this same columns in second query to do union or you need to remove this column to do union operation

Answer 3

As the error says, the first part has 7 columns, and the second part has only 4. An unions needs to have the same columns on both sides. Either remove

b.AlarmingStatus ,b.STxModel ,c.GroupID 

from the first part, or add (even bogus) columns in the second part.

Answer 4

Your first query is selecting 7 columns where as the second query is only selecting 4. You need to make sure the second query is selecting the same number of columns as the first to make the Union All work.

SELECT a.ESN, a.UnixTime, a.Payload, a.Timestamp
                ,b.AlarmingStatus
                ,b.STxModel
                ,c.GroupID
                FROM STxMessage a
                JOIN STx b ON b.ESN = a.ESN
                JOIN GroupInfo c ON b.GroupID = c.GroupID
                WHERE b.STxModel = 190
                AND a.AlarmsChecked="y"
                AND c.AlertsMasterSwitch="on"
               UNION ALL 
      SELECT d.ESN , d.UnixTime,  d.Payload,  d.Timestamp, 'null' as AlarmingStatus,
      'null' as STxModel, 'null' as GroupID FROM STxMessageArchive d