Qualifying fields is adding one ore more constraints on some of the columns. The qualification syntax is identical to the <&ASU.home|ASU> protocol:

Some typical examples:

keep only non-blank (i.e. specified, or not-null) values:
restrict a number to the range 12.0 to 12.5: 
	12.0 .. 12.5 
restrict a date to before June 1, 1997: 
	< 1997.06.01 
restrict a stellar spectral type ((char) column) to early types:

1  Numeric fields

The following table describes all operators available on numeric fields (i.e. not flagged by (char)):

=Strict equality (default)=10
>=Greater or equal>=10
>Strictly greater>10
<=Smaller or equal<=10
<Strictly smaller<10
..Range of numbers5..10
&AND (logical operator)1..5 & 7..9
|OR (logical operator)1..5 | 7..9
,List of values0,1,2
!NOT (logical operator)! 1..5

2  Values in Numeric fields

What follows the comparison operators are generally numbers; in a few cases, several ways of writing values are possible:

nullUnspecified (blank)value (<0)|null
now Current date and time (DATE only) < now
RA Sexagesimal hours, minutes, seconds of time 23 56 .. 00 04
Right ascension in decimal degrees 359 .. 001
DE Sexagesimal degrees, minutes, seconds of arc +41 45 .. +42 30
Declination in decimal degrees +41.75 .. +42.50
DATE/TIME UT Date and time, alphabetic month >= 1-Jan-1996
UT Date and Time, numeric month >= 1996.01.01 00:00:00
Julian Date >=JD2450083.5