PRECEDES
Purpose
Evaluates two Period expressions or derived periods, or DateTime expressions to TRUE, FALSE, or UNKNOWN.
Syntax
where:
|
Syntax element... |
Specifies... |
|
period_expression |
any expression that evaluates to a Period data type. Note: The Period expression specified must be comparable with the other expression. Implicit casting to a Period data type is not supported. |
|
datetime_expression |
any expression that evaluates to a DATE, TIME, or TIMESTAMP data type. |
|
derived_period |
any expression that evaluates to a derived period. |
Result Value
Error Conditions
If either expression is other than a Period data type or a DateTime value expression, an error is reported.
If the Period expressions are not comparable, an error is reported.
Example
Assume the following query is executed on the employee table where period1 and period2 are PERIOD(DATE) columns:
SELECT * FROM employee WHERE period1 PRECEDES period2;
|
ename |
period1 |
period2 |
|
Adams |
('2005-02-03', '2006-02-03') |
('2005-02-03', '2006-02-03') |
|
Mary |
('2005-04-02', '2006-01-03') |
('2005-02-03', '2006-02-03') |
|
Jones |
('2004-01-02', '2004-03-05') |
('2004-03-05', '2004-10-07') |
|
Randy |
('2004-01-02', '2004-03-05') |
('2004-03-07', '2004-10-07') |
|
Simon |
? |
('2005-02-03', '2005-07-27') |
The result is:
|
ename |
period1 |
period2 |
|
Jones |
('2004-01-02','2004-03-05') |
('2004-03-05', '2004-10-07') |
|
Randy |
('2004-01-02','2004-03-05') |
('2004-03-07', '2004-10-07') |
Example
Assume in the employee table, created by the following CREATE TABLE statement, jobdur1 and jobdur2 are derived period columns.
CREATE TABLE employee (
eid INTEGER NOT NULL,
name VARCHAR(100) NOT NULL,
deptno INTEGER NOT NULL,
jobst1 DATE NOT NULL,
jobend1 DATE NOT NULL,
PERIOD FOR jobdur1(jobst1, jobend1),
jobst2 DATE NOT NULL,
jobend2 DATE NOT NULL,
PERIOD FOR jobdur2(jobst2, jobend2)
) PRIMARY INDEX(eid);
|
EID |
Name |
DeptNo |
JobSt1 |
JobEnd1 |
JobSt2 |
JobEnd2 |
|
1 |
Tom |
101 |
DATE'2001-01-01' |
DATE'2004-01-01' |
DATE'2005-01-01' |
DATE'2006-01-01' |
|
2 |
Rick |
201 |
DATE'2005-01-01' |
DATE'2006-01-01' |
DATE'2001-01-01' |
DATE'2004-01-01' |
|
3 |
Joo |
301 |
DATE'2005-01-01' |
DATE'2006-01-01' |
DATE'2006-01-01' |
DATE'2007-01-01' |
|
4 |
Tam |
401 |
DATE'2001-01-01' |
DATE'2006-01-01' |
DATE'2002-01-01' |
DATE'2004-01-01' |
|
5 |
Pat |
501 |
DATE'2005-01-01' |
DATE'2007-01-01' |
DATE'2006-01-01' |
DATE'2008-01-01' |
|
6 |
Jack |
601 |
DATE'2005-01-01' |
DATE'2007-01-01' |
DATE'2007-01-01' |
DATE'2008-01-01' |
|
7 |
Yu |
701 |
DATE'2005-01-01' |
DATE'2007-01-01' |
DATE'2004-01-01' |
DATE'2005-01-01' |
|
8 |
Tim |
801 |
DATE'2005-01-01' |
DATE'2007-01-01' |
DATE'2005-01-01' |
DATE'2007-01-01' |
In the following SQL statement, PRECEDES is used with derived period columns of the employee table:
SELECT eid, name, jobst1, jobend1, jobst2, jobend2
FROM employee
WHERE jobdur1 PRECEDES jobdur2;
The result is:
|
EID |
Name |
DeptNo |
JobSt1 |
JobEnd1 |
JobSt2 |
JobEnd2 |
|
1 |
Tom |
101 |
DATE'2001-01-01' |
DATE'2004-01-01' |
DATE'2005-01-01' |
DATE'2006-01-01' |
|
3 |
Joo |
301 |
DATE'2005-01-01' |
DATE'2006-01-01' |
DATE'2006-01-01' |
DATE'2007-01-01' |
|
6 |
Jack |
601 |
DATE'2005-01-01' |
DATE'2007-01-01' |
DATE'2007-01-01' |
DATE'2008-01-01' |