Database Toolbox

Working with Cell Arrays in MATLAB

When you import data from a database into MATLAB, the data is stored as a numeric matrix, a structure, or a MATLAB cell array, depending on the data return format preference you specified using setdbprefs or the Database Toolbox Preferences dialog box.

Once the data is in MATLAB, you can use MATLAB functions to work with it. Because some users are unfamiliar with cell arrays, this section provides a few simple examples of how to work with the cell array data type in MATLAB:

• Viewing Cell Array Data Returned from a Query
• Viewing Elements of Cell Array Data
• Performing Functions on Cell Array Data
• Creating Cell Arrays for Exporting Data from MATLAB

For more information on using cell arrays, see Structures and Cell Arrays in the MATLAB documentation.

Viewing Cell Array Data Returned from a Query

Viewing Query Results

1. How you view query results depends on if you imported the data using the fetch function or if you used the Visual Query Builder.
• If you imported data using the fetch function, MATLAB returns, for example (see Exporting Data from MATLAB to a New Record in a Database)

•     curs =
          Attributes: []
                Data: [3x1 double]
      DatabaseObject: [1x1 database]
            RowLimit: 0
            SQLQuery: 'select freight from orders'
             Message: []
                Type: 'Database Cursor Object'
           ResultSet: [1x1 sun.jdbc.odbc.JdbcOdbcResultSet]
              Cursor: [1x1 com.mathworks.toolbox.database.sqlExec]
           Statement: [1x1 sun.jdbc.odbc.JdbcOdbcStatement]
               Fetch: [1x1
                      com.mathworks.toolbox.database.fetchTheData]
  

• The retrieved data is in the field Data. To view it, type

  •     curs.Data
    

  Alternatively, you can assign the data to a variable, for example, A, by typing

  •     A = curs.Data
    

  and then view it by typing A.

• If you imported data using the Visual Query Builder, you assign the results to the workspace variable, which is A in this example, using the Visual Query Builder. To see the data, type the workspace variable name at the MATLAB prompt in the Command Window, for example, type A.
2. MATLAB displays the data in the Command Window, for example

• A = 
     32.3800
     11.6100
     65.8300
  

Viewing Results with Multiple Columns

If the query results consist of multiple columns, you can view all the results for a single column using a colon (:). See the example in Exporting Multiple New Records from MATLAB. For example, you view the results of column 2 by typing

• A(:,2)
  

or if you used fetch, you can also view it by typing

• curs.Data(:,2)
  

MATLAB returns the data in column 2, for example

• ans =
          1400
          2400
          1800
          3000
          4300
          5000
          1200
          3000
          3000
             0
  

Expanding Results

If the results do not fit in the display space available, MATLAB expresses them as an array. If for example, MATLAB returns these query results.

• B = 
      [122]    'Virgina Power' 
      [123]    'North Land Trading' 
      [124]              [1x20 char]
      [125]    'Bush Pro Shop' 
  

You can see the data in rows 1, 2, and 4, but the second column in row 3 is expressed as an array because the results are too long to display.

To view the contents of the second column in the third row, type

• B(3,2)
  

or if you used fetch, you can also view it by typing

• curs.Data(3,2)
  

MATLAB returns

• ans = 
      'The Ristuccia Center'
  

About Objects and Methods for the Database Toolbox

Viewing Elements of Cell Array Data