Convert Nvarchar DD/MM/YYYY to YYYY-MM-DD in SQL Query - sql

Question

Hi I have a column in my 'Users' table called 'PersonalDetails_DOB'.
The data type is a NVARCHAR(10) and the 'format' the data is currently in DD/MM/YYYY.
I want to change the format to YYYY.MM.DD or YYYY-MM-DD, how would I do this?
I have already tried a running a query in SQL:
SELECT CONVERT(nvarchar(10), PersonalDetails_DOB, 102) as
'PersonalDetails_DOB' FROM Users;
Nothing happens and it doesn't change any date from e.g. 06/02/1967 to 1967.02.06

Answer 1

You need two convert() function :
SELECT PersonalDetails_DOB,
CONVERT(VARCHAR(10), CONVERT(DATE, PersonalDetails_DOB, 103), 102)
FROM Users;

Answer 2

Store dates as dates, not strings. I recommend you pull the value as a date and not a string:
SELECT CONVERT(date, PersonalDetails_DOB, 103) as PersonalDetails_DOB
FROM Users;
You are safer using try_convert():
SELECT TRY_CONVERT(date, PersonalDetails_DOB, 103) as PersonalDetails_DOB
FROM Users;
To find the bad values, you can do:
select PersonalDetails_DOB
from users
where TRY_CONVERT(date, PersonalDetails_DOB, 103) is null;
You can convert back a string if you want.
I would recommend that you fix the data structure. This should work:
update users
set PersonalDetails_DOB = CONVERT(date, PersonalDetails_DOB, 103);
alter users alter column PersonalDetails_DOB date;

Answer 3

You can try the below query to update the date values format and also their data type using SUBSTRING() function as shown below
declare #PersonalDetails_DOB NVARCHAR(10)
set #PersonalDetails_DOB = '13/10/2018' --dd/MM/yyyy
select SUBSTRING(#PersonalDetails_DOB,7,4) + '-' + SUBSTRING(#PersonalDetails_DOB,4,2)
+ '-' + SUBSTRING(#PersonalDetails_DOB,1,2)
-- yyyy-MM-dd
create table Users(PersonalDetails_DOB NVARCHAR(10))
insert into Users values ('01/10/2018')
select * from Users --Before Update
--Updating date values
update Users
set PersonalDetails_DOB = (
SUBSTRING(#PersonalDetails_DOB,7,4) + '-' + SUBSTRING(#PersonalDetails_DOB,4,2)
+ '-' + SUBSTRING(#PersonalDetails_DOB,1,2)
)where PersonalDetails_DOB is not null
select * from Users --After Update
--Change the datatype
ALTER TABLE Users
ALTER COLUMN PersonalDetails_DOB date;
You can find the live demo Live Demo Here

Answer 4

Maybe you should first set dateformat before conversion:
set dateformat dmy;
select PersonalDetails_DOB
,convert(nvarchar(10), cast(PersonalDetails_DOB as datetime), 102) as ANSI_DOB
,convert(nvarchar(10), cast(PersonalDetails_DOB as datetime), 120) as ODBC_DOB
from Users;