HP 3000 Manuals HP 3000 Manuals
Comparison Predicate
A comparison predicate compares two expressions using a comparison
operator. The predicate evaluates to TRUE if the first expression is
related to the second expression as specified in the comparison operator.
Scope
SQL Data Manipulation Statements
SQL Syntax
{= }
{<>}
Expression {> } [Expression]
{>=} [SubQuery ]
{< }
{<=}
Parameters
Expression specifies a value used to identify columns,
screen rows, or define new column values. The
syntax of expressions is defined in the
"Expressions" chapter. Both numeric and
non-numeric expressions are allowed in comparison
predicates. Predicates cannot include LONG
columns.
SubQuery is a QueryExpression whose result is used in
evaluating another query. The syntax of
QueryExpression is presented in the description
of the SELECT statement.
= is equal to. A comparison predicate using = is
also known as an EQUAL predicate.
<> is not equal to.
> is greater than.
>= is greater than or equal to.
< is less than.
<= is less than or equal to.
Description
* Character strings are compared according to the HP eight-bit ASCII
collating sequence for ASCII data, or the collation rules for the
native language of the DBEnvironment for NLS data. Column data
would either be ASCII data or NLS data depending on how the column
was declared upon its creation. Constants are ASCII data or NLS
data depending on whether you are using NLS or not.
If a case insensitive ASCII expression is compared to a case
insensitive NLS expression, the two expressions are compared using
the NLS collation rules. The case insensitive NLS comparison is
done by using the NLSCANMOVE and NLSCOLLATE intrinsics. The same
ASCII characters in upper and lower case are equivalent. Accent
characters (extended character) in upper and lower case are also
equivalent. However, an accent character may not be the same as
its ASCII equivalent, depending on the specific language collation
table.
Extended upper and lower case characters are not equivalent to the
ASCII expression. They are compared to the NLS collation table.
If a case sensitive character column is compared to a character
column that is not case sensitive, both columns are treated as
case sensitive. If a string constant is compared to a column that
is not case sensitive, then the string constant is treated as not
case sensitive.
* Refer to the "Data Types" chapter for type conversion that
ALLBASE/SQL
performs when you compare values of different types.
* For purposes of the Comparison Predicate, a NULL value on either
or both sides of the predicate causes it to evaluate to unknown.
Thus, two NULL values on either side of an equals predicate will
not result in a TRUE result but rather in unknown.
* A NULL value in an expression causes comparison operators to
evaluate to unknown. Refer to the "Search Condition" section at
the beginning of this chapter for more information on evaluation
of operators.
* A subquery must return a single value (one column of one row). If
the subquery returns more than one value, an error is given. If
the subquery returns no rows, the predicate evaluates to unknown.
Example
The part numbers of parts that require fewer than 20 days for delivery
are retrieved.
SELECT PartNumber
FROM PurchDB.SupplyPrice
WHERE DeliveryDays < 20