Oracle SQL Where条款对日期列

Question

I have a DATE column with a date in it but I need to query it to find records less than 30 days old.

START_DATE
----------
01-AUG-2010
09-AUG-2010
22-AUG-2010
09-SEP-2010

Query:

SELECT START_DATE
 WHERE START_DATE < 30;

I know it is simple Query in ORACLE SQL but i am doing something wrong.

Answer 1

Use:

SELECT t.start_date
  FROM YOUR_TABLE t
 WHERE t.start_date > SYSDATE - 30

• SYSDATE is Oracle's syntax to get the current date and time
• In Oracle, you can do date arithmetic in the context of days, so SYSDATE - 30 means "current date, subtract thirty days" to get a date that is thirty days in the past

If you want to evaluate the date based on thirty days as of midnight, use the TRUNC function :

SELECT t.start_date
  FROM YOUR_TABLE t
 WHERE t.start_date > TRUNC(SYSDATE) - 30

Don't run TRUNC on the column - that will render an index on the column useless, ensuring a table scan.

Answer 2

SELECT t.start_date
  FROM YOUR_TABLE t
 WHERE t.start_date > SYSDATE - INTERVAL '30' DAY;

INTERVAL is more portable than assuming that you can add or subtract days, although I've noticed some slight differences in the INTERVAL syntax between Oracle and PostgreSQL.

Answer 3

WHERE START_DATE > SYSDATE - 1

or perhaps

WHERE TRIM(STARTDATE) > TRIM(SYSDATE) - 1