Defining Selection


Given a table of values, such as C.Wunsch's data from GEOSECS Station 3: 
	press    temp    sal      O2     Sigma0
	---------------------------------------
	  5.000  18.334  33.570   5.970  24.096
	 25.000  12.848  34.159   6.990  25.773
	 49.000  11.070  34.523   6.060  26.394
	 99.000  11.093  35.090   5.340  26.831
	149.000  11.906  35.487   5.020  26.990
        ...
A selection can be defined as choosing record instances which satisfy certain criteria. In other words, a selection determines which rows to include in operations which follow.

Example:
Your selection is: press > 50
The result is: 
	press    temp    sal      O2     Sigma0
	---------------------------------------
	 99.000  11.093  35.090   5.340  26.831
	149.000  11.906  35.487   5.020  26.990
        ...

Defining Projection

A projection can be defined as choosing which parameters to use from among all available parameters. In other words, you can determine to see only some of the columns in a table.

Example:
Your projection is: press, temp, O2
The result is: 
	press    temp     O2
	_____________________ 
	  5.000  18.334   5.970
	 25.000  12.848   6.990
	 49.000  11.070   6.060
	 99.000  11.093   5.340
	149.000  11.906   5.020
        ...
These two query types can be used in combination to further specify a subselection.
[Back] Return to Help on Subselections