sql date

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SQL Date

  • SQL Date

    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

    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

    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!

  • 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!

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