尝试退出联接时出现意外结果

Question

I have this SQL statement which works fine..

SELECT result=count(j.client_id), j.client_id 
FROM spp_job j  
GROUP BY j.client_id 
ORDER BY  count(j.client_id) DESC

but failed when I use LEFT JOIN

SELECT result=count(j.client_id), c.name 
FROM spp_job j 
LEFT JOIN spp_client c ON j.client_id = c.id  
GROUP BY j.client_id 
ORDER BY count(j.client_id) DESC

I don't know what went wrong. I want to show the client name instead of their id. The second SQL give me all client records.

Answer 1

Since you are listing c.name with the left join, you need to Group By c.name instead j.client_id

SELECT result=count(j.client_id), c.name 
FROM spp_job j LEFT JOIN
    spp_client c ON j.client_id = c.id  
GROUP BY c.name 
ORDER BY result DESC

UPDATE: Since name is not unique (as @lc. said) you may need to use group by both by id and name for accurate results.

GROUP BY j.client_id, c.name 
ORDER BY result DESC

Answer 2

I think you want to get the NAME for every client_id .

you also need to add name in the GROUP BY clause because the column is not aggregated ,

SELECT  result = count(j.client_id), 
        c.name 
FROM    spp_job j 
        LEFT JOIN spp_client c 
            ON j.client_id = c.id  
GROUP   BY j.client_id, c.name
ORDER   BY result DESC

Answer 3

You are running into a Sybase extension to the standard behavior of GROUP BY . From the documentation (see halfway down the page at "Transact-SQL extensions to group by and having"):

Transact-SQL extensions to standard SQL make displaying data more flexible, by allowing references to columns and expressions that are not used for creating groups or summary calculations:

• A select list that includes aggregates can include extended columns that are not arguments of aggregate functions and are not included in the group by clause. An extended column affects the display of final results, since additional rows are displayed.

  • The group by clause can include columns or expressions that are not in the select list.

...

When the Transact-SQL extensions add rows and columns to a display, or if group by is omitted, query results may be hard to interpret.

The example from that page explains what happens:

The Transact-SQL extended column, price (in the select list, but not an aggregate and not in the group by clause), causes all qualified rows to display in each qualified group, even though a standard group by clause produces a single row per group. The group by still affects the vector aggregate, which computes the average price per group displayed on each row of each group (they are the same values that were computed for example a)

Note that the standard behavior of GROUP BY does not allow this and will produce an error to the effect of "Use of non-aggregated column not specified in group-by clause".

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For your query, you should also group by c.name as JW. suggests .