Date Functions in SQL Server and MySQL

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# SQL Date Functions

## 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 complicated.

Before talking about the complications of querying for dates, we will look at the most important built-in functions for working with dates.

## MySQL Date Functions

The following table lists the most important built-in date functions in MySQL:

Function | Description
--- | ---
NOW() | Returns the current date and time
CURDATE() | Returns the current date
CURTIME() | Returns the current time
DATE() | Extracts the date part of a date or date/time expression
EXTRACT() | Returns a single part of a date/time
DATE_ADD() | Adds a specified time interval to a date
DATE_SUB() | Subtracts a specified time interval from a date
DATEDIFF() | Returns the number of days between two dates
DATE_FORMAT() | Displays date/time data in different formats

## SQL Server Date Functions

The following table lists the most important built-in date functions in SQL Server:

Function | Description
--- | ---
GETDATE() | Returns the current date and time
DATEPART() | Returns a single part of a date/time
DATEADD() | Adds or subtracts a specified time interval from a date
DATEDIFF() | Returns the time between two dates
CONVERT() | Displays date/time data in different formats

## 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:MM:SS
- TIMESTAMP - format: YYYY-MM-DD HH:MM: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:MM:SS
- SMALLDATETIME - format: YYYY-MM-DD HH:MM:SS
- TIMESTAMP - format: a unique number

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

For an overview of all data types available, go to our complete Data Types reference.

## SQL Working with Dates

You can compare two dates easily if there is no time component involved!

Assume we have the following "Orders" table:

OrderId | ProductName | OrderDate
--- | --- | ---
1 | Geitost | 2008-11-11
2 | Camembert Pierrot | 2008-11-09
3 | Mozzarella di Giovanni | 2008-11-11
4 | Mascarpone Fabioli | 2008-10-29

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:

OrderId | ProductName | OrderDate
--- | --- | ---
1 | Geitost | 2008-11-11
3 | Mozzarella di Giovanni | 2008-11-11

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

OrderId | ProductName | OrderDate
--- | --- | ---
1 | Geitost | 2008-11-11 13:23:44
2 | Camembert Pierrot | 2008-11-09 15:45:21
3 | Mozzarella di Giovanni | 2008-11-11 11:12:01
4 | Mascarpone Fabioli | 2008-10-29 14:56:59

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: If you want to keep your queries simple and easy to maintain, do not allow time components in your dates!

From http://www.w3schools.com (Copyright Refsnes Data)