Why do I need to use different syntax to access the results of my SQL query with Database Toolbox 3.2 (R2006b) than with earlier versions?

I have the following code to retrieve data from my database

setdbprefs('DataReturnFormat','cellarray');

curs = exec(conn, sql);

curs=fetch(curs);

clprice=[curs.Data{:,2}];

With Database Toolbox 3.2 (R2006b), this last statement returns only one element although I have multiple elements in curs.Data as verified by the following output

 K>> curs.Data

 ans =

     'A-NBP-GasY05'           [ 4.7031e+009]

     'A-NBP-GasY06'           [ 5.4298e+009]

     'A-NBP-GasY07'           [ 5.3461e+009]

     'A-NBP-GasY08'           [ 4.8868e+009]

     'A-NBP-Sm06'             [ 3.3269e+009]

     'A-NBP-Sm07'             [ 4.3463e+009]

     'A-NBP-Sm08'             [ 4.2863e+009]

     'A-NBP-Wn06-07'          [ 6.5192e+009]

The same line of code would return the entire first column in earlier versions of Database Toolbox.

Answer 1

[MathWorks Support Team]

This change in behavior is due to an incompatibility introduced in MATLAB 7.3 (R2006b). This change was introduced to fix a bug related to indexing in cell arrays.

The change is that when "a" is a cell array, x = a{:,1} no longer throws an error but returns the first element of the output. This is now the desired behavior both in Database Toolbox and MATLAB.

If you wish to retrieve a column of data as a matrix, use the CELL2MAT function when all of the data in the Data field is numeric.

For example , instead of typing

[curs.Data{:,1}]

use

cell2mat(curs.Data(:,1))

Also, when using the Data property of a cursor object, it is not possible to return multiple outputs when using the cell indexing notation {}.

For example:

[a,b]=curs.Data{:,2}

returns the error message

 ??? Error using ==> cursor.subsref

 Too many output arguments.

If you with to return multiple outputs from the Data cell array, you will need to create a temporary copy of the Data field and then perform the indexing.

x=curs.Data;

[a,b]=x{:,1}

This will display the output

 a =

      1

 b =

      2

For more information on the bug that was fixed see the following Bug Report http://www.mathworks.com/support/bugreports/details.html?rp=301697