Question

I have the below query, which basically it retrieves the 5 top most books sold:

    select top 5 count(id_book_orddetails) 'books_sold', bk.*     from orderdetails_orddetails ord inner join books_book bk     on ord.id_book_orddetails = bk.id_book     group by id_book, name_book,author_book,desc_book,id_ctg_book,qty_book,image_book,isdeleted      order by 'books_sold' desc  

The problem is that I am receiving this error:

The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.

In the books_book table, the field desc_book is of type ntext, and I’m sure that the problem is coming from there.

This is because before I changed the desc_book to ntext, it was of type nvarchar and it worked perfectly.

The reason I changed the data type of this field is because somehow in PHP website, when I was displaying the book description (a different sp), the description was being truncated to about 200-255 characters, thus I changed it to ntext and it ‘solved my problem’ (ie, the whole desc_book was finally being displayed).

So basically these are my questions :

1. Why is the desc_book (nvarchar) field being truncated when displayed in a PHP page?
2. How can i fix the SQL query to accommodate for grouping by an ntext field?

Just for the record (which I don’t think is very relevant), I am using MS SQL Server 2005

[UPDATE]

I tried and tested both of Bill Karwin‘s proposed solutions and they both work perfectly. I thus decided in grouping the count aggregate result into a subquery…ie’s Karwin’s latter solution.

So here is my updated (fully working) statement:

SELECT bk.*, bc.books_sold FROM books_book bk INNER JOIN (     SELECT bk2.id_book, COUNT(*) books_sold     FROM books_book bk2      INNER JOIN orderdetails_orddetails ord      ON (bk2.id_book = ord.id_book_orddetails)     GROUP BY bk2.id_book ) bc ON (bk.id_book = bc.id_book) ORDER BY books_sold desc; 

Answer 1

The old PHP ‘mssql’ extension only supports VARCHAR up to 255 bytes in size. This is a known limitation, and it’s why Microsoft has been developing a new PHP extension to support modern SQL Server releases.

One workaround is to declare the storage of that column as NVARCHAR, but when you query it from PHP, use CAST to convert it to NTEXT. Then the full length can be returned.

Another option is to keep the column stored as NTEXT, but GROUP BY only book_id by putting the count into a subquery:

SELECT bk.*, bc.books_sold FROM books_book bk   INNER JOIN (SELECT bk2.book_id, COUNT(*) books_sold       FROM books_book bk2 INNER JOIN orderdetails_orddetails ord          ON (bk2.id_book = ord.id_book_orddetails)       GROUP BY bk2.book_id) bc     ON (bk.book_id = bc.book_id);