How to Generate a Range of Dates in SQL Using CONNECT BY, CROSS JOIN, or Stored Procedures?

How to Use SQL to Generate a Range of Dates

When working with SQL, it's often necessary to run queries across multiple dates. This can be challenging if you don't have a predefined list of dates to work with. Fortunately, there are several techniques you can use to generate a range of dates in SQL.

One common approach is to use the CONNECT BY clause. This clause allows you to create a hierarchical query that generates a series of rows based on a specified relationship. For example, the following query will generate a list of the last 365 days:

SELECT TRUNC(SYSDATE - ROWNUM) dt
FROM DUAL CONNECT BY ROWNUM < 366

This query starts with the current date (SYSDATE) and then subtracts one day for each row in the hierarchy. The ROWNUM pseudo-column keeps track of the current row number, and the CONNECT BY clause ensures that the query will stop after generating 365 rows.

Another option for generating a range of dates is to use the CROSS JOIN operator. This operator allows you to combine two tables into a single result set, even if they don't have any matching columns. For example, the following query will generate a list of all possible combinations of days and hours:

SELECT day, hour
FROM (
  SELECT LEVEL - 1 day
  FROM DUAL CONNECT BY LEVEL <= 365
)
CROSS JOIN (
  SELECT LEVEL - 1 hour
  FROM DUAL CONNECT BY LEVEL <= 24
)

This query starts by creating a table of days (the first subquery) and a table of hours (the second subquery). The CROSS JOIN operator then combines these two tables into a single result set, generating all possible combinations of days and hours.

Finally, you can also use a stored procedure to generate a range of dates. A stored procedure is a set of SQL statements that are stored in the database and can be executed multiple times. The following stored procedure will generate a list of the last 365 days:

CREATE PROCEDURE generate_dates AS
BEGIN
  FOR i IN 1 .. 365 LOOP
    INSERT INTO dates (dt) VALUES (TRUNC(SYSDATE - i));
  END LOOP;
END;

This stored procedure can be executed by calling the following statement:

EXECUTE generate_dates;

Once the stored procedure has been executed, you can then use the dates table to run your queries.

These are just a few of the techniques you can use to generate a range of dates in SQL. The best approach for you will depend on the specific needs of your application.

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