|
In Query By
Form (QBF) format, the columns of ONE table can be queried. In its
simplest form, the field values determine the query condition:
ABC
Which results in this
query:
SELECT *
FROM <table>
WHERE <column> =
'ABC'
Wildcards, operators, and
special characters can be used to refine the query:
|
Token
|
Description
|
Example
|
Resulting where clause
|
|
%
|
Wildcard
|
H%
|
<column> LIKE 'H%'
|
|
*
|
Wildcard
|
H*
|
<column> LIKE 'H%'
|
|
_
|
Wildcard
|
H_H
|
<column> LIKE 'H_H'
|
|
?
|
Wildcard
|
H?H
|
<column> LIKE 'H_H'
|
|
NULL
|
NULL
|
NULL
|
<column> IS NULL
|
|
\
|
Escape
|
\<TAG\>
|
<column> = '<TAG>'
|
|
\\
|
\
|
\\AND\%
|
<column> = '\AND%'
|
The following table describes
the operators that can be used:
|
Token
|
Description
|
Field filling
|
Resulting where clause
|
|
<
|
Less than
|
< 5
|
<column> < 5
|
|
<=
|
Less equal
|
<= 5
|
<column> <= 5
|
|
=
|
Equal
|
= 5
|
<column> = 5
|
|
>
|
Greater
|
> 5
|
<column> > 5
|
|
>=
|
Greater equal
|
>= 5
|
<column> >= 5
|
|
!
|
Not
|
!ABC
|
NOT (<column> = 'ABC')
|
|
|
|
!>5
|
NOT(<column> > 5)
|
|
|
|
!ABC%
|
NOT(<column> LIKE 'ABC%')
|
|
&
|
And
|
>5 & <10
|
<column> > 5 AND <column> < 10
|
|
|
|
Or
|
5 | 6
|
<column> = 5 OR <column> = 6
|
|
()
|
Nesting of conditions
|
!(5 | 6)
|
NOT (<column> = 5 OR <column> = 6)
|
|
|
|
(>5 & < 7)|
(>10 & < 20)
|
( <column> > 5 AND <column> < 7) OR
(<column> > 10 AND
<column> < 20)
|
|
AND
|
And
|
|
|
|
OR
|
Or
|
|
|
|
·
|
'AND' and 'OR' are aliases for the '&' and '|' operators
and can be used everywhere where these operators can be used. |
|
·
|
<, <=, =, > are comparison operators. These operators
are followed by a value. In combination with this value they form a
Boolean expression. |
|
·
|
A value on itself without a comparison operator is also a
Boolean expression. It implicitly uses the '=' operator. |
|
·
|
&, |, AND, OR are logical operators. These operators are
preceded and followed by a Boolean expression. With these
expressions they form a new Boolean expression. |
|
·
|
! is a unary operator. This operator expects a Boolean
expression on the right side. With this expression it forms a
Boolean expression. |
|
·
|
() encapsulates a Boolean expression. |
|
·
|
In a YACC (Yet Another Compiler-Compiler) parser-like notation
the definition of the syntax allowed is: |
expression :
VALUE
| <
VALUE
|
<= VALUE
| =
VALUE
| >
VALUE
|
>= VALUE
| !
expression
|
expression & expression
|
expression | expression
| (
expression )
|
expression AND expression
|
expression OR expression
;
|
