Query builder
This is probably main part of the QVarStar. Here you enter query which
is used by QVarStar to make selection from catalog. Query is logical
expression built by terms that can be combined with logical
operations (you have example queries on the bottom of this page). There are two kind of operators:
- Relational operators
- '=' - equal
- '<' - less than
- '>' - greater than
- Logical operators
- '&' - logical and
- '|' - logical or
Relational operators
You can use this operators to compare specific field with some
value.
Fields can have one of this types:
- Integer (123)
- Real (123.456)
- Character ('c')
- String ("string")
In parentheses you have example how to enter values of specific type.
There are two rules you should respect:
- Comparing field and value must be with same type (e.g. you
can't compare "integer" field with "string" or "real" value)
- You can't use all three relational operators with every field
type. (e.g. with "string" and "character" type you can use only "=" operator)
Logical operators
Result of relational operator applied on field and value operands is
boolean value "true" or "false". That values can be combined with
logical operators "&" and "|". Logical and ("&") has higher priority than
logical or ("|"). If you want to override this priority you can use
parentheses.
Examples