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The MQL Preview button allows the user to preview the data that will be returned from the MQL Query. In order for the preview to function properly, your Pentaho BI Server must be running. Prior to release 1.6.M5 preview was not functional. A preliminary fix, requiring manual configuration of JNDI connections, has been made in version 1.6.M5 that corrects this issue. To enable MQL Preview functionality create the following directory <workspace-dir>/.metadata/.plugins/org.pentaho.designstudio.editors.actionsequence/simple-jndi. In this director create a jdbc.propertiess properties file and define the jndi connection name used in the metadata file. A sample jndi definition is shown below:
SampleData/type=javax.sql.DataSource
SampleData/driver=org.hsqldb.jdbcDriver
SampleData/url=jdbc:hsqldb:hsql://localhost/sampledata
SampleData/user=pentaho_user
SampleData/password=password
You'll also have to make sure that the JDBC driver jar file for the database you are trying to use is on your Java classpath. The easiest way to do this is to drop the jar in the <JAVA_HOME>/lib directory.
Once this is done MQL queries can be previewed.
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