Changing the format of data in a column - sql

Question

Trying the change the date column from YYYYMMDD to MMDDYYYY while maintaining varchar value. Currently my column is set as varchar(10). Is there a way to change the strings in mass numbers because I have thousands of rows that need the format converted.
For example:
| ID | Date |
------------------------
| 1 | 20140911 |
| 2 | 20140101 |
| 3 | 20140829 |
What I want my table to look like:
| ID | Date |
------------------------
| 1 | 09112014 |
| 2 | 01012014 |
| 3 | 08292014 |
Bonus question: Would it cause an issue while trying to convert this column if there is data such as 91212 for 09/12/2012 or something like 1381 which is supposed to be 08/01/2013?

Answer 1

Instead of storing the formatted date in separate column; just correct the format while fetching using STR_TO_DATE function (as you said your dates are stored as string/varchar) like below. Again, as other have suggested don't store date data as string rather use the datetime data type instead
SELECT STR_TO_DATE(`Date`, '%m/%d/%Y')
FROM yourtable
EDIT:
In that case, I would suggest don't update your original table. Rather store this formatted data in a view or in a separate table all together like below
create view formatted_date_view
as
SELECT ID,STR_TO_DATE(`Date`, '%m/%d/%Y') as 'Formatted_Date'
FROM yourtable
(OR)
create table formatted_date_table
as
SELECT ID,STR_TO_DATE(`Date`, '%m/%d/%Y') as 'Formatted_Date'
FROM yourtable
EDIT1:
In case of SQL Server use CONVERT function like CONVERT(datetime, Date,110). so, it would be (Here 110 is the style for mm-dd-yyyy format)
SELECT ID,convert(datetime,[Date],110) as 'Formatted_Date'
FROM yourtable
(OR)
CAST function like below (only drawback, you can't use any specific style to format the date)
SELECT ID, cast([Date] as datetime) as 'Formatted_Date'
FROM yourtable

Answer 2

MS SQL Server Solution:
Which SQL are you trying with?
MSSQL Server 2008 R2
You can use Convert function on your date field. You have to specify the date's format Style.
For mm/dd/yyyy format Style value is 101.
Using with style value, your update statement can be:
UPDATE table_name
SET date = CONVERT( VARCHAR, date, 101 )
Refer To:
How to format datetime & date in Sql Server
SQL Server 2008 Date Format
Demo # MS SQL Server 2008 Fiddle
MySQL Solution:
it needs to stay in varchar or int and the dates are yyyymmdd and I need to change thousands of rows of data to be in mmddyyyy format.
Change to date type using str_to_date and then change again to string using date_format.
UPDATE table_name
SET date = DATE_FORMAT( STR_TO_DATE( date, '%Y%m%d' ), '%m%d%Y' )
The value 20140911 when converted from yyyymmdd to mmddyyyy format, will retain the leading 0 as 09112014.
Bonus question: Would it cause an issue while trying to convert this column if there is data such as 91212 for 09/12/2012 or something like 1381 which is supposed to be 08/01/2013
You can use str_to_date( '91212', '%c%e%y' ) to convert the same to valid date object. But MySQL, though defines to support single digit month and date numbers, it won't parse such date correctly and returns a NULL on such formats.
mysql> select str_to_date( '91212', '%c%e%y' ) s1, str_to_date( '091212', '%c%e%y' ) s2;
+------+------------+
| s1 | s2 |
+------+------------+
| NULL | 2012-09-12 |
+------+------------+
1 row in set, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+------------------------------------------------------------+
| Level | Code | Message |
+---------+------+------------------------------------------------------------+
| Warning | 1411 | Incorrect datetime value: '91212' for function str_to_date |
+---------+------+------------------------------------------------------------+
1 row in set (0.00 sec)