The form to set constraints, and choose which parameters to display, needs some expertise... It is powerful, but we recommend to read the following introduction before getting discouraged by the lack of success.
When issued after a first selection, this form allows the user to combine the initial constraints with further restrictions, or when starting directly with this form, the constraints will apply to the whole catalogue.
For example, you may have selected all the spectra for the stars HD190007 and HD400, and then you want to select only those with a S/N exceeding 200.
At the bottom of the result page of the first request appears a list of all the fields of the table, with a form offering to set constraints.
In this form, simply fill the constraint for sn26 as: > 200 and submit.
You will get the list of spectra for HD190007 and HD400 having S/N > 200
Suppose now that you want to retrieve all the high S/N spectra (say sn26 > 250 ) for equatorial stars (say -1 > dec < +1 deg). In the form, you will fill the constraints for dec and sn26 respectively with BETWEEN -1 and +1 and > 250. When you submit it, you will get this.
The constraints have to be written directly in SQL, the language of the database server. Some of the most common constraints you may like to use are:
| SQL statement | Example | Explanation |
|---|---|---|
| = | fiber = 'HR' | equality |
| != | view_spec != 'not public' | not equal |
| IS NULL | get_spec IS NULL | does not have a value |
| IS NOT NULL | get_spec IS NOT NULL | has a value |
| IN | mask IN ('F8', 'G0') | is in a list of values |
| < | sn26 < 200 | less than, also ≤ |
| > | exptime > 300 | greater than, also ≥ |
| BETWEEN | ra BETWEEN -10 AND 10 | in a range of values |
| LIKE | mask LIKE 'G2%' | pattern matching, % is a wildcard |