116 SQL Dates

Here’s a summary of the current webpage on “Date Functions in SQL Server and MySQL”:

• Date Handling in SQL: The page explains challenges with date formatting in SQL—especially making sure the dates you insert match the database's column format.
• Date Data Types:
  • MySQL: Supports DATE, DATETIME, TIMESTAMP, YEAR with formats like YYYY-MM-DD and YYYY-MM-DD HH:MI:SS.
  • SQL Server: Supports DATE, DATETIME, SMALLDATETIME, and a TIMESTAMP (which is a unique number, not a date).
• Using Dates in Queries:
  • Simple queries work if only the date part is stored.
  • If there’s a time component, direct equality queries (e.g., WHERE OrderDate = 'YYYY-MM-DD') may not match any rows unless the time is also exactly the same.
• Best Practice: Avoid storing time with your date, unless necessary, to keep queries simpler.
• Examples Provided:
  • Table data demonstrates how querying works with and without time components.
• Quiz: There’s a quiz to check the correct DATE data type format (correct answer: YYYY-MM-DD).

Overall, the page gives practical guidelines and examples for handling dates in SQL for both MySQL and SQL Server, focusing on how different formats affect querying and storage.[1]

1

SQL Dates

The most difficult part when working with dates is to be sure that the format of the date you are trying to insert, matches the format of the date column in the database.

As long as your data contains only the date portion, your queries will work as expected. However, if a time portion is involved, it gets more complicated.

SQL Date Data Types

MySQL comes with the following data types for storing a date or a date/time value in the database:

• DATE - format YYYY-MM-DD
• DATETIME - format: YYYY-MM-DD HH:MI:SS
• TIMESTAMP - format: YYYY-MM-DD HH:MI:SS
• YEAR - format YYYY or YY

SQL Server comes with the following data types for storing a date or a date/time value in the database:

• DATE - format YYYY-MM-DD
• DATETIME - format: YYYY-MM-DD HH:MI:SS
• SMALLDATETIME - format: YYYY-MM-DD HH:MI:SS
• TIMESTAMP - format: a unique number

Note: The date types are chosen for a column when you create a new table in your database!

SQL Working with Dates

Look at the following table:

Orders Table

Now we want to select the records with an OrderDate of "2008-11-11" from the table above.

We use the following SELECT statement:

SELECT * FROM Orders WHERE OrderDate='2008-11-11'

The result-set will look like this:

Note: Two dates can easily be compared if there is no time component involved!

Now, assume that the "Orders" table looks like this (notice the added time-component in the "OrderDate" column):

If we use the same SELECT statement as above:

SELECT * FROM Orders WHERE OrderDate='2008-11-11'

we will get no result! This is because the query is looking only for dates with no time portion.

Tip: To keep your queries simple and easy to maintain, do not use time-components in your dates, unless you have to!