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Convert Datetime string to date in SQL Server

I have a datetime data from C# like this
2019-03-20T11:25:32.0342949
I tried to convert it to datetime using cast and it triggers error
select cast('2019-03-20T11:25:32.0342949' as date)
Conversion failed when converting date and/or time from character string.
I guess its because of the T in the string.
I tried format also which of course doesn't work because its not identify it as date.
So how can I convert it properly to date. Without some substring methods to extract the date part.

You have to use DATETIME2 instead of DATETIME:
SELECT CAST('2019-03-20T11:25:32.0342949' AS DATETIME2) -- 2019-03-20 11:25:32.0342949
demo on dbfiddle.uk
The issue is the precision of the milliseconds part of your string value. You are using seven digits on the milliseconds part which is not possible on DATETIME. So you can do two things:
shorten the milliseconds part to three digits and use DATETIME
use DATETIME2 for more precision
Use the time, date, datetime2 and datetimeoffset data types for new work. These types align with the SQL Standard. They are more portable. time, datetime2 and datetimeoffset provide more seconds precision. datetimeoffset provides time zone support for globally deployed applications.
source: https://learn.microsoft.com/en-us/sql/t-sql/data-types/datetime-transact-sql
There is also a comparison between DATETIME and DATETIME2 on StackOverflow:
DateTime2 vs DateTime in SQL Server

If you need only date this will work
select cast('2019-03-20T11:25:32.0342949' as date) As DATE
If you need date and time this will work
select cast('2019-03-20T11:25:32.0342949' as datetime2) As DATE
Tried in Sql 15 Its working

You have to take advantage of the CONVERT() method. For example, SELECT CONVERT(date, getdate()), with date being the string you just mentioned. In your case, your datetime string takes up 10 letters of string, so you could also do SELECT CONVERT(VARCHAR(10), GETDATE(), 103). The 3rd parameter is the datetime style you want to convert to.

You should not pass datetime as string from C#, this is the correct way to pass:
string sql = "SELECT * FROM table WHERE datevalue= #date";
SqlParameter dateParam = new SqlParameter("#date", SqlDbType.DateTime);
dateParam .Value = dateValue;
SqlCommand command = new SqlCommand(sql);
command.Parameters.AddWithValue("#date", dateParam );
// then execute the command...

How to use DateTime with SQL queries?

How should I be using c# datetime values in my C# queries?
Up until now I've been doing the following:
Datetime my_time = new DateTime(2012, 09, 05);
cmd.Parameters.AddWithValue("#date", my_time);
cmd.CommandText = "SELECT * FROM sales WHERE date = #date";
Which has been working fine until this morning when I've been getting null errors when retrieving values from the results set.
I changed my date parameter to grab the short date string from my datetime value like this:
cmd.Parameters.AddWithValue("#date", my_time.ToShortDateString());
And it appears to be working fine again.
What is the correct way of doing this? Obviously I'm converting my datetime value to a string, only (presumably) for the database to convert it back to a datetime before evaluating my equality where clause, which seems a little pointless.
Edit:
I'm using SQL Server Compact Edition and the date field in my example has a precision setting of 8 (date, excluding time right?). Does that mean I was passing the full date with 00:00:00.000 on the end before? How might I pass a datetime value to the database without including the time, without converting to a string first?

You can just try with my_time.Date
cmd.Parameters.AddWithValue("#date", my_time.Date);

Do not pass it as a string or will run in troubles with culture formatting.
Try using SqlDateTime instead.

You're not converting the date to a string - AddWithValue knows it is a date, but it is a datetime, so it has a time component. Do your sales have a time component to them?
SELECT * FROM sales WHERE DateDiff(d, #date, date) = 0

String value to be inserted in a date datatype mysql

I want to insert current date into a database in the field cur_dt having datatype date.
string curr_dat= DateTime.Now.ToString("yyyy-mm-dd");
Can i insert curr_dat which is a string variable into a column cur_dt having datatype as date?
If not than how can i do it? How to define a date variable.I want to also insert current time in the a column cur_tm having datatype time.
Please help me to understand how to insert the date and time into the database.

If you write SQL like
INSERT INTO foo SET bar='<date here>'
or similar, you can use both parameters or just String.Format to put the date there as a STring.
Additionally, if you want to put the current Date/Time there, why not just use
INSERT INTO foo SET bar=now() -- if column type is datetime
INSERT INTO foo SET bar=CURDATE() -- if column type is date
and have the database set in the correct date in the correct form

read mysql date/time functions here http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html

You would need to convert curr_dat variable to DateTime before assigning it to cur_dt column. You can also create a new DateTime value is following way
DateTime curDate = new DateTime(DateTime.Now.Year,DateTime.Now.Month, DateTime.Now.Day,0,0,0);
and assign the value to cur_dt column.

str_to_date(string_data, format)
STR_TO_DATE('Dec/15/2011', '%M/%d/%Y'); => 2011-12-15

Oracle date formatting

in my c# programme i am requesting data from an oracle database and one field is the date abd time in this format - 12/09/2008 15:11:17 , is there anyway i can just return the date?
Is there also a way of ensuring its in british format, by modifying the sql to be dd/mm/yyyy
thanks

You could get the date part of the DateTime using C#, You could do
string date = MyDateTime.ToString("dd/MM/yyyy");///let MyDateTime be your DateTime variable
If you want to do in Oracle, you can use to_char for example,
select to_char(sysdate, 'dd/MM/yyyy') From dual;

The Oracle trunc() function removes the time part:
select trunc(datecol) from mytable;

In your sql query to oracle you can
to_date('12/09/2008 15:11:17', 'dd/MM/yyyy')
where you replace the date with your field in the oracle db.
Alternatively, you can handle it on the C# side with formatting
CultureInfo ukCulture = new CultureInfo("en-GB");
//this assuming you do not have a datetime type
DateTime myDateTime = DateTime.Parse("12/09/2008 15:11:17", ukCulture.DateTimeFormat);
string result = myDateTime.ToString(ukCulture.DateTimeFormat.ShortDatePattern));

C#+linq - Inserting DateTime value to the Db in the right format

I have a Db server with DateTime fields in the format of "yyyy-MM-dd mm:hh:ss"
I'm trying to use linq2sql to insert a DateTime member to a DateTime field in one of my tables.
When I do it in SQL I convert the DateTime as following:
"Insert into .... Convert(datetime, getdate(), 120) ..."
But when I try to submit the object from Linq the date time inserts in the wrong format.
Is there a way to define the format that will be inserted to the Db in Linq?
Or is it a DateTime object Issue?

You shouldn't be dealing with a string format when you pass dates and times to the database, any more than you would if you were passing a number. The database should be handling all this for you without any conversions. This is true whether you're using LINQ or within the SQL - almost any time you have to manually do string conversions between types at the database level, you should look for a better solution.
If you read the value back out of the database (as a DateTime again) does it have the right value? If not, in what way is it wrong?