Oracle SQL: Finding Date or Closest Date to Specified Date

When working with dates in Oracle, there are various scenarios where you need to find the closest date to a specified date. In this article, we will explore two common use cases:

1. Finding the record with the exact date in the table.
2. Finding the maximum or minimum date that is closest to but not greater than a specified date.

Background

Oracle provides several functions and operators for working with dates, including:

• TO_DATE: Converts a string value to a date value.
• DATE_TRUNC: Truncates a date value to a specific date format.
• EXTRACT: Extracts components from a date value using various functions such as EXTRACT(YEAR FROM , EXTRACT(MONTH FROM , etc.).
• ADD_MONTHS: Adds months to a date value.

These functions and operators can be used in combination with the SQL language to perform complex date-related operations.

Finding the Record with the Exact Date

To find the record with the exact date in the table, you can use an equality comparison operator (=) between two date values. However, when working with dates, it’s essential to consider time zones and daylight saving time (DST) rules.

In the provided example, the query uses a subquery to extract the exchange rate for each record:

SELECT EXCHANGE_RATE
FROM ISET.PREVIOUS_PRICES
WHERE SECURITY_ID = E.SECURITY_ID
  AND VAL_DATE = TO_DATE('05/08/2019', 'DD/MM/YYYY')

This query will only return records where the VAL_DATE matches the specified date exactly.

However, there are scenarios where you might want to find the record with the closest date that is not greater than a specified date. This can be achieved using various techniques:

Using ROWNUM

One approach is to use ROWNUM to select the first row from the result set. You can modify the query as follows:

SELECT *
FROM (
  SELECT *, ROW_NUMBER() OVER (ORDER BY TO_DATE('05/08/2019', 'DD/MM/YYYY') - VAL_DATE DESC) AS RN
  FROM PREVIOUS_PRICES b
  WHERE SECURITY_ID = E.SECURITY_ID
    AND status_date <= TO_DATE ('05/08/2019', 'DD/MM/YYYY')
)
WHERE RN = 1

This query uses ROW_NUMBER to assign a ranking to each row based on the difference between the specified date and the record’s date. The first row with the smallest positive difference is selected.

Using MIN or MAX

Another approach is to use aggregate functions like MIN or MAX to find the closest date:

SELECT MIN(b.val_date) AS CLOSEST_DATE
FROM PREVIOUS_PRICES b
WHERE SECURITY_ID = E.SECURITY_ID
  AND status_date <= TO_DATE ('05/08/2019', 'DD/MM/YYYY')

This query returns the minimum VAL_DATE value that meets the condition. However, this approach assumes that you want to find the closest date before the specified date.

Using LEAST or GREATEST

You can also use aggregate functions like LEAST (minimum) or GREATEST (maximum) to achieve the desired result:

SELECT LEAST(b.val_date, TO_DATE('05/08/2019', 'DD/MM/YYYY'))
FROM PREVIOUS_PRICES b
WHERE SECURITY_ID = E.SECURITY_ID

This query returns the smallest value between the record’s date and the specified date.

Finding the Closest Date Below a Specified Date

To find the closest date below a specified date, you can use various approaches:

Using MIN with a CASE Statement

One approach is to use a CASE statement with aggregate functions like MIN to find the closest date that meets the condition:

SELECT MIN(TO_DATE('05/08/2019', 'DD/MM/YYYY') - b.val_date) AS CLOSEST_DATE
FROM PREVIOUS_PRICES b
WHERE SECURITY_ID = E.SECURITY_ID
  AND status_date < TO_DATE ('05/08/2019', 'DD/MM/YYYY')

This query returns the minimum difference between the specified date and each record’s date. The first row with the smallest positive difference is selected.

Using GREATEST or LEAST

You can also use aggregate functions like GREATEST (maximum) or LEAST (minimum) to achieve the desired result:

SELECT GREATEST(TO_DATE('05/08/2019', 'DD/MM/YYYY'), b.val_date)
FROM PREVIOUS_PRICES b
WHERE SECURITY_ID = E.SECURITY_ID

This query returns the largest value between the specified date and each record’s date.

Using a Correlated Subquery

Another approach is to use a correlated subquery to find the closest date:

SELECT b.val_date
FROM PREVIOUS_PRICES b
WHERE SECURITY_ID = E.SECURITY_ID
  AND status_date < TO_DATE ('05/08/2019', 'DD/MM/YYYY')
AND b.val_date > (
  SELECT MIN(b2.val_date)
  FROM PREVIOUS_PRICES b2
  WHERE SECURITY_ID = E.SECURITY_ID
    AND status_date < TO_DATE ('05/08/2019', 'DD/MM/YYYY')
)

This query returns the minimum VAL_DATE value that meets the condition.

Conclusion

Finding dates in Oracle SQL can be a complex task, especially when dealing with multiple conditions and comparisons. In this article, we explored various approaches to find records with exact or closest dates:

• Using equality comparison operators (=) for exact matches.
• Using aggregate functions like MIN or MAX to find closest dates.
• Using ROWNUM, LEAST, or GREATEST to select the first row or largest/smallest value.

These techniques can be applied to various date-related operations in Oracle SQL, making it easier to work with dates and improve the performance of your queries.

Last modified on 2024-08-10