The SQL Search Condition declares a condition that results in FALSE, TRUE, or UNKNOWN.
search-condition ::=
boolean-value-expression
boolean-value-expression ::=
boolean-term
| boolean-value-expression OR boolean-term
boolean-term ::=
boolean-factor
| boolean-term AND boolean-factor
boolean-factor ::=
[ NOT ] boolean-test
boolean-test ::=
boolean-primary [ IS [ NOT ] truth-value ]
truth-value ::=
TRUE | FALSE | UNKNOWN
boolean-primary ::=
predicate
| nonparenthesized-value-primary
| ( boolean-value-expression )
In SQL, boolean expressions use 3-state logic, which can result in one of three values: FALSE, TRUE, or UNKNOWN. UNKNOWN is returned when one or more values are NULL.
The truth table of the AND operator:
| AND | True | False | Unknown |
|---|---|---|---|
| True | True | False | Unknown |
| False | False | False | False |
| Unknown | Unknown | False | Unknown |
The truth table of the OR operator:
| OR | True | False | Unknown |
|---|---|---|---|
| True | True | True | True |
| False | True | False | Unknown |
| Unknown | True | Unknown | Unknown |
The truth table of the IS operator:
| IS | True | False | Unknown |
|---|---|---|---|
| True | True | False | False |
| False | False | True | False |
| Unknown | False | False | True |
To find all analog voltage tags that are less than 23.5 volts:
Select FullName,Value
From TagDataPointAnalog
Where Units = 'Volts' AND Value < 23.5
To learn more about the SQL features in Fernhill SCADA.
For the meaning of terms used in Fernhill SCADA.