15.00 - PRECEDES - Teradata Database

Teradata Database SQL Functions, Operators, Expressions, and Predicates

Product
Teradata Database
Release Number
15.00
Content Type
Programming Reference
Publication ID
B035-1145-015K
Language
English (United States)
Last Update
2018-09-24

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

  • If both expressions have a Period data type or a derived period, the function returns TRUE if the ending bound of the first expression is less than or equal to the beginning bound of the second expression; otherwise, the function returns FALSE.
  • If the first expression is a Period expression and the second expression is a DateTime expression, the function returns TRUE if the ending bound of the first expression is less than or equal to the second expression; otherwise, the function returns FALSE.
  • If the first expression is a DateTime expression and the second expression has a Period data type, the function returns TRUE if the first expression is less than the beginning bound of the second expression; otherwise, the function returns FALSE.
  • If either expression is NULL, the operator returns UNKNOWN.
  • 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'