SQL查询显示添加到表中的最新数据

Question

I have a SQL query that displays the latest data that was recently added into the database. This is the query :

SELECT Name, Picture, briefDescription from table order by DatePosted desc limit 1

My problem is, the data that was given to me was not the latest data in the database, it gave me an old entry instead. My DataPosted format is of DateTime and in the database, it is of type String. Any ideas why? Thanks in advance!

Answer 1

If DatePosted is of type string in the database, then it will sort alphabetically, and not by date. Change the DatePosted field to type DATETIME (or equivalent) in the database, and your code should work.

For example, here is a set of sample data selected using a string DatePosted field. As you can see, it is not sorting descendingly.

SELECT * FROM TestTable ORDER BY DatePosted DESC

Id  Name    DatePosted
3   Charlie 10/12/2013 10:03:56 PM
2   Bravo   10/11/2013 9:03:56 PM
6   Delta   10/11/2013 9:03:56 AM
1   Alpha   10/11/2013 10:03:56 PM

You will most likely need to write a script to convert the data from string to DATETIME, as most DBMSs (perhaps all) will not allow you to convert a string column type to a numeric type such as DATETIME implicitly. You can perform this conversion in a number of ways. Perhaps the easiest way would be to add a new column of type DATETIME, copy the data from the string column to the new DATETIME column, remove the string column, and change the name of the new column to DatePosted.

Here's an example that will perform this conversion:

UPDATE TestTable SET DatePosted2 = CAST(DatePosted AS DATETIME)

And the new results:

SELECT * FROM TestTable ORDER BY DatePosted DESC

Id  Name    DatePosted
3   Charlie 2013-10-12 22:03:56.000
1   Alpha   2013-10-11 22:03:56.000
2   Bravo   2013-10-11 21:03:56.000
6   Delta   2013-10-11 09:03:56.000

Answer 2

instead of changing value in your database you can just cast the date in your SQL statement for the correct order:

SELECT Name, Picture, briefDescription 
FROM table 
ORDER BY CAST(DatePosted AS DATETIME) desc limit 1