MATLAB DATABASE TOOLBOX RELEASE NOTES Guía de usuario descargar pdf (Pagina 383)

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101

Selecting Data Using the exec Function

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• A cursor stays open until you close it using the close function.

Working with Microsoft Excel

For Microsoft Excel, tables in sqlquery are Excel worksheets. By default, some

worksheet names include $. To select data from a worksheet with this name format, use

an SQL statement of the form select * from "Sheet1$" (or 'Sheet1$') .

Database Considerations

• The order of records in your database is not constant. Use values in column names to

identify records. Use the SQL ORDER BY command to sort records.

• Before you modify database tables, ensure that the database is not open for editing. If

you try to edit the database while it is open, you receive this MATLAB error:

[Vendor][ODBC Driver] The database engine could not lock

table 'TableName' because it is already in use by

another person or process.

• You might experience issues with text field formats in the Microsoft SQL Server

database management system. Workarounds for these issues are as follows:

• Convert fields of format NVARCHAR, TEXT, NTEXT, and VARCHAR to CHAR in the

database.

• Use sqlquery to convert data to VARCHAR. For example, run a sqlquery

statement of the form 'select convert(varchar(20),field1) from

table1'.

• The PostgreSQL database management system supports multidimensional fields, but

SQL select statements fail when retrieving these fields unless you specify an index.

• Some databases require that you include a symbol, such as #, before and after a date

in a query as follows:

curs = exec(conn,'select * from mydb where mydate > #03/05/2005#')

• Some databases require that you include a symbol, such as #, before and after a date

in a query as follows:

curs = exec(conn,'select * from mydb where mydate > #03/05/2005#')

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