使用左连接和计数查询在MySQL中的选择工作但在MS SQL Server 2012中没有

Question

I have the following two tables:

SURVEY
id: INT (PK)
title: VARCHAR
description: TEXT

QUESTIONNAIRE
id: INT (PK)
title: VARCHAR
survey_id: INT (FK on survey.id)

Screenshot of tables

I want to sellect all surveys along with the number of questionnaires that each survey has so i tried the following query:

SELECT s.id, s.title, s.description, count(q.id)  
FROM  survey s  
LEFT OUTER JOIN questionnaire q  ON q.survey_id = s.id  
GROUP BY s.id

I tried the query in MySQL and it works great.
The problem is i need to use MS SQL SERVER 2012 where the same query does not work.

First i got the following error:

Msg 8120, Level 16, State 1, Line 1 Column 'survey.title' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause

.

then i tried:

 SELECT s.id, s.title, s.description, count(q.id)  
 FROM  survey s  
 LEFT OUTER JOIN questionnaire q  
   ON q.survey_id = s.id  
 GROUP BY s.id, s.title, s.description

which reslted in the following error:

Msg 306, Level 16, State 2, Line 4 The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.

If i remove the s.description (which is TEXT) from the SELECT and GROUP BY the query works but this is no solution.

Any ideas ? Thank you

Answer 1

I think you should learn how Group By and aggregate functions work. This would prove greatly effective in your quest to understanding T-SQL. Here is a link that may help you out.

Group By Information

Also, this may not be the case at all but why Text for the description and not varchar in MS SQL Server 2012?

Answer 2

text is deprecated - try nvarchar(max) or varchar(max)

ntext, text, and image (Transact-SQL)

The left may be the problem but I get you want it.

If nvarchar(max) or varchar(max) does not fix it then try this

SELECT s.id, s.title, s.description, sq.cc  
 FROM  survey s  
 join ( SELECT ss.id, count(qq.id) as cc 
          FROM  survey ss  
          LEFT OUTER JOIN questionnaire q  
                ON q.survey_id = s.id  
         GROUP BY s.id 
      ) sq 
   on sq.id = s.id 

Answer 3

您使用聚合函数和非聚合函数，您必须将表与自身连接，并在要计数的列上使用group by函数

Answer 4

The problem is your Description column type :

Msg 306, Level 16, State 2, Line 4 The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.

If you change the type of the column to nvarchar(max) you will be able to perform your group by.

Answer 5

As well as changing the column datatype in the table (or casting to VARCHAR(MAX) at run time) you could also use

SELECT s.id,
       s.title,
       s.description,
       COALESCE(q.cnt,0) AS cnt
FROM   survey s
       LEFT OUTER JOIN (SELECT COUNT(q.id) AS cnt,
                               q.survey_id
                        FROM   questionnaire q
                        GROUP  BY q.survey_id) q
                    ON q.survey_id = s.id 

to avoid having to GROUP BY that column at all