I am using Microsoft SQL Server Management Studio to manipulate Public transport system database.
I have a table in database named 'dbo.tblStop_times', two columns of which should be of data type time. At the moment, they are both nvarchar and they have data stored in a pattern like this - "07:39:00" (without quotes)
I had same question with date columns as well, but found a solution for that on stackoverflow just few hours back.
Below works fine for conversion of nvarchar column to date column.
ALTER TABLE tblCalendar ALTER COLUMN [start_date] DATE NOT NULL;
I am not sure if what I want is achievable or not, because the above mention conversion works just fine, I assume it might be possible.
What I have atm is - nvarchar(8), what I want it to be is sql time data type, something like hh:mm:ss [and if possible - without trailing nnnnnn - nanoseconds component]
You should be able to do:
ALTER TABLE tblStop_times ALTER COLUMN start_time TIME NOT NULL;
Here is a rextester.
EDIT:
If you don't have valid time values, then you have a problem. You should first look for the values:
select col
from tblStop_times
where try_convert(time, col) is null;
This will show you the values that cannot be converted. If you like, you can NULL them out so the alter will work:
update tblStop_times
set col = NULL
where try_convert(time, col) is null;
Related
I'm working on a table with a column, 'Expiry Date', as a varchar with all data formatted as DD/MM/YYYY.
The creator of the table has used the wrong type for this expiry date column and now the client needs to filter and show all records before and after the current date as the time. This means the type needs to be changed to date or datetime type to be able to use the CURDATE() function.
However, the current format of the values does not satisfy and wont allow the type to change unless the format is changed to YYYY-MM-DD (or similar).
Is there any way to mass format the values in this column and this column alone as there are thousands of entries and formatting one by one would be extremely time consuming.
Let me assume that you are using MySQL.
Perhaps the simplest method is to add a generated column that is a date:
alter table t add column expiry_date_date as
(str_to_date(expiry_date, '%d/%m/%Y'));
You can also fix the data:
update t
set expiry_date = str_to_date(expiry_date, '%d/%m/%Y');
This will implicitly convert the result of str_to_date() to a date, which will be in the YYYY-MM-DD format.
More importantly, you can then do:
alter table t modify column expiry_date date;
Here is a db<>fiddle.
You can do similar operations in other databases, but the exact code is a bit different.
What you need is an update on that column, but before doing it I suggest you to check if the result is what you want.
select replace(expiry_date, '/', '-') new_expiry_date
from table_name
If this returns the results you want you can run the following update:
update table_name
set expiry_date = replace(expiry_date, '/', '-')
Of course you will need to replace expiry_date and table_name with the names of your column and table.
I have 3 tables in the database that I'm working on. Out of 3, two of the tables have columns that include dates. When I checked the information schema of the columns I found that dates have the wrong data type. If you see the picture below, the highlighted columns should be stored as DATE data type.
So, I used the following query to change their data type from varchar to DATE:
ALTER TABLE [dbo].[Customer]
ALTER COLUMN DOB DATE;
ALTER TABLE [dbo].[Transactions]
ALTER COLUMN tran_date DATE;
The error that I get is:
Conversion failed when converting date and/or time from character string.
Please let me know how I can fix this error. Thanks!
What you can do is update the value using try_convert() first and then alter the column name. Note: This will set any invalid values to NULL.
update customer
set dob = try_convert(date, dob);
alter table customer alter column dbo date;
If you want to see the bad values, then before you change the table, run:
select c.*
from customer c
where try_convert(date, dob) is null and dob is not null;
You may have other ideas on how to fix the values.
You can't change from varchar to date or time or datetime by altering the column. Why? Because SQL Server does not know if the field contains '1/1/2020' or 'My dog is cute'. You will have to rebuild the table with the proper data types and then CAST() or CONVERT() the values to a true date time.
Underneath the hood, this makes more sense. A char/varchar uses one byte per character. nchar/nvarchar uses 2 bytes per character. A datetime is a number, not a character. This means you need a routine that changes this into the correct number. If you want to get deeper, the number is the number of ticks (nanoseconds) since midnight on January 1, 0001 in the Gregorian Calendar. More info.
I have an issue where I created a column sent_Date of type nvarchar while it's storing date and time.
Now when I try to sort it by date, it's not doing so correctly.
I am using this query:
select *
from tbl_skip
where sent_date > '9/27/2020 7:29:11 PM'
order by SENT_DATE desc
Like the comments have said, the real solution here is fix your design. That means changing the column's data type an nvarchar to a date and time data type, I'm going to use a datetime2(0) here, as your data is accurate to a second, so seems the most appropriate.
Firstly we need to convert the value to as ISO value. I'm also, however, going to create a new column called Bad_Sent_Date, to store values that could not be converted. Experience has taught many of us that systems that incorrectly use string data types to store dates (or numerical data) rarely have good data integrity rules on the value (because if they did, it wouldn't be an nvarchar) to start, so have bad values like '29/02/2019' or mix styles, such as having both '09/29/2020' and '29/09/2020'.
Based on the single example we have, I will assume your data is supposed to be in the format MM/dd/yy hh:mm:ss AM/PM:
ALTER TABLE dbo.tbl_skip ADD Bad_Sent_Date nvarchar(30) NULL;
GO
UPDATE TABLE dbo.tbl_skip
SET Bad_Sent_Date = CASE WHEN TRY_CONVERT(datetime2(0),Sent_date,101) IS NULL THEN Sent_date END,
Sent_Date = CONVERT(nvarchar(30),TRY_CONVERT(datetime2(0),Sent_date,101),126);
GO
Now we have an ISO format, we can change the table's data type:
ALTER TABLE dbo.tbl_skip ALTER COLUMN Sent_date datetime2(0) NULL;
Note that if you do have constraints on the column Sent_date, or it isn't NULLable, you will first need to DROP said CONSTRAINTs, change the column to be NULLable and then recreate said CONSTRAINTs after you have altered the column.
You can also review the "dates" that failed to be converted with the following:
SELECT bad_sent_date
FROM dbo.tbl_skip
WHERE bad_sent_date IS NOT NULL
AND Sent_date IS NULL;
Once that's all done, then your query simply needs an update to use an unambiguous date literal, and it'll work:
SELECT *
FROM tbl_skip
WHERE sent_date > '2020-09-27T19:29:11' --'9/27/2020 7:29:11 PM'
ORDER BY SENT_DATE DESC;
You can convert the data from string to datetime.
Please note i used 100 as an example to convert to date time. You can use below link to see if its behaving correctly. link -https://www.w3schools.com/sql/func_sqlserver_convert.asp
select *
from tbl_skip
where sent_date > convert(datetime,'9/27/2020 7:29:11 PM',100)
ORDER BY CONVERT(datetime,SENT_DATE,100) desc
You should be able to convert it to a datetime
select *
from tbl_skip
where sent_date > '9/27/2020 7:29:11 PM'
order by convert(datetime,SENT_DATE) desc
Just make sure the data in column is legit. If so, it would make sense to convert the column type to a datetime.
alter table tbl_skip alter column SENT_DATE datetime
If the data is mixed, you may need to fix it or use something like
order by try_convert(datetime,SENT_DATE) desc
I have a column in Oracle DB which is varchar2 data type. Typical value stored in this column is like 06/16/2015 02:14:18 AM.
I am trying to get all records wherein this column is having records after 1st August 2015.
select *
from MYTABLE
where to_date(substr(MYCOLUMN,1,10),'dd-mm-yyyy') > to_date('01-08-2015','dd-mm-yyyy');
But, I am getting ORA-01843. Where am I doing wrong?
Respect the format in your VARCHAR
....where to_date(substr(MYCOLUMN,1,10),'mm/dd/yyyy')
I have a column in Oracle DB which is varchar2 data type. Typical value stored in this column is like 06/16/2015 02:14:18 AM.
The first question is why do you store DATE as string? Using appropriate data type is one of the most important part of database design and performance.
Understand that DATE doesn't have the format you see, it is internally stored in 7 bytes which is Oracle's proprietary format. Storing date as a string to have a fixed format is not recommended.
I would suggest first fix the design so that you don't have to do this overhead activity while comparing dates. In the longer run it will help you.
1. Add a new column as DATE data type.
ALTER TABLE table_name
ADD new_column DATE;
2. Update the new column.
UPDATE table_name
SET new_column = TO_DATE(old_column, 'mm/dd/yyyy hh:mi:ss pm');
3. DROP the old column.
ALTER TABLE table_name
DROP COLUMN old_column;
4. Rename the new column to old column name.
ALTER TABLE table_name
RENAME COLUMN old_name to new_name;
Now, you could compare dates easily:
SELECT * FROM MYTABLE WHERE mycolumn > to_date('01-08-2015','dd-mm-yyyy');
This will also use any regular index on the date column.
From performance point of view:
If you don't fix it now, you will keep facing performance issues. Because the immediate fix of SUBSTR will not let you use any regular index, you need to create a function-based index.
If in your table all values like 06/16/2015 02:14:18 AM then you can use trunc(to_date(MYCOLUMN,'mm/dd/yyyy HH:mi:SS PM'),'dd') against to_date(substr(MYCOLUMN,1,10),'dd-mm-yyyy').
How do i combine 2 column using SQL server 2005 ?
Problem is that The DateTime is stored in 1 column and the milliseconds is stored in another column.
I want to add the Milliseconds onto DateTime column to give it a more accurate DateTime.
I need to use this DateTime to query record accurate to milliseconds.
Any idea?
I need to replace DateTime with the added values.
SELECT *
FROM TABLENAME
WHERE [DateTime] >= '2011-04-12 12:00:00 AM'
AND [DateTime] <= '2011-05-25 3:35:04 AM'
and run the query.
Well, first solve your problem:
SELECT DATEADD(millisecond,<milliscolumn>,<datetimecolumn>) from <table>
And then file a bug report that these should just be stored in one column anyway.
You can do this, based on your sample query, but note that this destroys the possibility of the server being able to use an index:
SELECT * FROM TABLENAME WHERE
DATEADD(millisecond,[MillisecondColumn],[DateTime]) between
'2011-04-12T12:00:00' AND '2011-05-25T03:35:04'
If this is a large table, then indexes may be important. If you can't alter whatever's populating this data, you might want to add this calculation as a persisted computed column to this table, and then index and query against that.
Note that I've replaced your two comparisons with a single BETWEEN, and also adjusted the datetime strings so that they're not affected by regional settings.
SELECT (ColumnA + ColumnB) AS ColumnZ
FROM Table
might solve your problem.