SQL SERVER – Adding Column Defaulting to Current Datetime in Table

Presenting a technical session is a greatest experience one can have and I enjoy doing the same. While I write this blog post, I am presenting at Great Indian Developer Summit in India. The event is a grand success and I am having a great time at this event. One of the questions which I often receive is how do one can add the column to existing table which will be auto-populated with the current datetime when the original row is inserted. There is indeed a simple solution to achieve this goal. One has to just create table with default value as a current datetime.

In following example we will first create a sample table and later we will add a column which will be defaulted to the current date time when any new record is inserted. The only drawback of this method is that if there is any existing row in your table it will be automatically have the current date time when the column is created. Honestly I do not see any solution to this issue as this is related to design of the database. If you know what was the datetime when rows were created you can update those rows with those value otherwise, just have any values stored there.

Let us see our solution. Let us first create a table which does not have column with current datetime. In our case we will assume that there are only two rows in the table.

USE tempdb
GO
-- Create Table
CREATE TABLE TestTable (ID INT, Col1 VARCHAR(100));
-- Insert Values
INSERT INTO TestTable (ID, Col1)
SELECT 1, 'First'
UNION ALL
SELECT 2, 'Second';
-- Select from table
SELECT *
FROM TestTable
GO

DateInserted1 SQL SERVER   Adding Column Defaulting to Current Datetime in Table

Now let us add a column to this table with default value as a current datetime. You will notice that the two rows which are inserted into the table have current datetime.

-- Add Column with Default Current Date Time
ALTER TABLE TestTable
ADD DateInserted DATETIME NOT NULL DEFAULT (GETDATE());
-- Select from table
SELECT *
FROM TestTable
GO

DateInserted2 SQL SERVER   Adding Column Defaulting to Current Datetime in Table

As a third step let us enter the a new row. Make sure that you do not insert any value in the newly created column where you have default value as a current date time.

-- Now Insert New Rows
INSERT INTO TestTable (ID, Col1)
SELECT 3, 'Third';
INSERT INTO TestTable (ID, Col1)
SELECT 4, 'Fourth';
GO
-- Select from table
SELECT *
FROM TestTable
GO

DateInserted3 SQL SERVER   Adding Column Defaulting to Current Datetime in Table

You will notice in the result set that the new column will contain current date time of the row created. This way you can get the value when the row was created.

Now you can clean up the resultset.

-- Clean up
DROP TABLE TestTable
GO

Here is the question back to you – “It is simple to create a column where we have default daytime value to know when the row was created. Is there any way to know when the row was updated without explicitly updating any column with datetime?”

Click to Download Scripts

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Difference Between CURRENT_TIMESTAMP and GETDATE() – CURRENT_TIMESTAMP Equivalent in SQL Server

A common question – I often get from Oracle/MySQL Professionals:

“What is the Equivalent to CURRENT_TIMESTAMP in SQL Server?”

Here is a common question I often get from SQL Server Professionals:

“What are differences between Difference Between CURRENT_TIMESTAMP and GETDATE ()?”

Very simple question but have showed up so frequently that I feel like to write about it.

Well in SQL Server GETDATE() is Equivalent to CURRENT_TIMESTAMP. However, if you use CURRENT_TIMESTAMP in your select statement it will work fine.

gdv SQL SERVER   Difference Between CURRENT TIMESTAMP and GETDATE()   CURRENT TIMESTAMP Equivalent in SQL Server

You can see in the above example – both of them returns the same value. Now let us go to next question regarding difference between GETDATE and CURRENT_TIMESTAMP. Well, the matter of the fact, there is no difference between them in SQL Server (Reference Link). CURRENT_TIMESTAMP is an ANSI SQL function, whereas GETDATE is T-SQL implementation of the same function. Both of them derive value from the operating system of the computer on which SQL Server instance is running.

Above discussion prompts another question – in this case, what should one use GETDATE or CURRENT_TIMESTAMP?

Well, this is indeed tricky and interesting question. I think I am very comfortable using the GETDATE () so I will go to use it but a matter of the fact there is no right or wrong answer. If you want to follow ancient saying “When in Rome, do as the Romans do”, I suggest using the GETDATE (), or continue using CURRENT_TIMESTAMP.

With that said, there is one very important property we all need to keep in mind. If you use CURRENT_TIMESTAMP while creating an object, they are automatically converted to GETDATE() and stored internally. To illustrate what I am suggesting here is the example –

Create a table using the following script

CREATE TABLE [dbo].[TestTable](
[Cold2] [datetime] NULL
)
ON [PRIMARY]
GO
ALTER TABLE [dbo].[TestTable] ADD DEFAULT (CURRENT_TIMESTAMP) FOR [Cold2]
GO

Now go to SSMS and generate the script for the table and you will notice following syntax.

CREATE TABLE [dbo].[TestTable](
[Cold2] [datetime] NULL
)
ON [PRIMARY]
GO
ALTER TABLE [dbo].[TestTable] ADD DEFAULT (GETDATE()) FOR [Cold2]
GO

You can notice that SQL Server have automatically converted CURRENT_TIMESTAMP to GETDATE(). I guess this gives us an idea how they behave. Now go ahead and make your choice! Do let me know which one will you use CURRENT_TIMESTAMP or GETDATE () in the comments area.

Click to Download Scripts

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Fix Error: Microsoft OLE DB Provider for SQL Server error ‘80040e07’ or Microsoft SQL Native Client error ‘80040e07’

I quite often receive questions where users are looking for solution to following error:

Microsoft OLE DB Provider for SQL Server error ‘80040e07’
Syntax error converting datetime from character string.

OR

Microsoft SQL Native Client error ‘80040e07’
Syntax error converting datetime from character string.

If you have ever faced above error – I have a very simple solution for you.

http://www.pinaldave.com/bimg/error-logo.jpgThe solution is being very check date which is inserted in the datetime column. This error often comes up when application or user is attempting to enter an incorrect date into the datetime field. Here is one of the examples – one of the reader was using classing ASP Application with OLE DB provider for SQL Server. When he tried to insert following script he faced above mentioned error.

INSERT INTO TestTable (ID, MyDate)
VALUES (1, '01-Septeber-2013')

The reason for the error was simple as he had misspelled September word. Upon correction of the word, he was able to successfully insert the value and error was not there. Incorrect values or the typo’s are not the only reason for this error. There can be issues with cast or convert as well. If you try to attempt following code using SQL Native Client or in your application you will also get similar errors.

SELECT CONVERT (datetime, '01-Septeber-2013', 112)

The reason here is very simple, any conversion attempt or any other kind of operation on incorrect date/time string can lead to the above error. If you not using embeded dynamic code in your application language but using attempting similar operation on incorrect datetime string you will get following error.

Msg 241, Level 16, State 1, Line 2
Conversion failed when converting date and/or time from character string.

Remember: Check your values of the string when you are attempting to convert them to string – either there can be incorrect values or they may be incorrectly formatted.

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Find Weekend and Weekdays from Datetime in SQL Server 2012

Yesterday we had very first SQL Bangalore User Group meeting and I was asked following question right after the session.

“How do we know if today is a weekend or weekday using SQL Server Functions?”

Well, I assume most of us are using SQL Server 2012 so I will suggest following solution. I am using SQL Server 2012’s CHOOSE function. It is

SELECT GETDATE() Today,
DATENAME(dw, GETDATE()) DayofWeek,
CHOOSE(DATEPART(dw, GETDATE()), 'WEEKEND','Weekday',
'Weekday','Weekday','Weekday','Weekday','WEEKEND') WorkDay
GO

getdatedisplay2 SQL SERVER   Find Weekend and Weekdays from Datetime in SQL Server 2012

You can use the choose function on table as well. Here is the quick example of the same.

USE AdventureWorks2012
GO
SELECT A.ModifiedDate,
DATENAME(dw, A.ModifiedDate) DayofWeek,
CHOOSE(DATEPART(dw, A.ModifiedDate), 'WEEKEND','Weekday',
'Weekday','Weekday','Weekday','Weekday','WEEKEND') WorkDay
FROM [Person].[Address] A
GO

getdatedisplay1 SQL SERVER   Find Weekend and Weekdays from Datetime in SQL Server 2012

If you are using an earlier version of the SQL Server you can use a CASE statement instead of CHOOSE function.

Please read my earlier article which discusses CHOOSE function and CASE statements. Logical Function – CHOOSE() – A Quick Introduction

Click to Download Scripts

Reference:  Pinal Dave (http://blog.SQLAuthority.com)

SQL SERVER – Function to Round Up Time to Nearest Minutes Interval

Though I have written more than 2300 blog posts, I always find things which I have not covered earlier in this blog post. Recently I was asked if I have written a function which rounds up or down the time based on the minute interval passed to it. Well, not earlier but it is here today.

Here is a very simple example of how one can do the same.

CREATE FUNCTION [dbo].[RoundTime] (@Time DATETIME, @RoundToMin INT)
RETURNS DATETIME
AS
BEGIN
RETURN
ROUND(CAST(CAST(CONVERT(VARCHAR,@Time,121) AS DATETIME) AS FLOAT) * (1440/@RoundToMin),0)/(1440/@RoundToMin)
END
GO

Above function needs two values. 1) The time which needs to be rounded up or down. 2) Time in minutes (the value passed here should be between 0 and 60 – if the value is incorrect the results will be incorrect.) Above function can be enhanced by adding functionalities like a) Validation of the parameters passed b) Accepting values like Quarter Hour, Half Hour etc.

Here are few sample examples.

SELECT dbo.roundtime('17:29',30)
SELECT dbo.roundtime(GETDATE(),5)
SELECT dbo.roundtime('2012-11-02 07:27:07.000',15)

When you run above code, it will return following results.

roundtime SQL SERVER   Function to Round Up Time to Nearest Minutes Interval

Well, do you have any other way to achieve the same result? If yes, do share it here and I will be glad to share it on blog with due credit.

Click to Download Scripts

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Retrieve SQL Server Installation Date Time

I have been asked this question a number of times and my answer always has been “Search online and you will find the answer.” Every single time someone follows my answer, he finds the accurate answer in just a few clicks. However, this question is getting very popular nowadays, so I decided to answer this question through a blog post.

I usually prefer creating my own T-SQL script but in today’s case, I have taken the script from the Web. I have seen this script in so many places that I do not know who the original creator is, so I’m not sure who should get credit for the script.

Question: How do I retrieve SQL Server Installation date?

Answer: Run the following query and it will give you the date of SQL Server Installation.

SELECT create_date
FROM sys.server_principals
WHERE sid = 0x010100000000000512000000

Question: I have installed SQL Server Evaluation version. How do I know what is the expiry date for it?

Answer: SQL Server evaluation period lasts for 180 days. The expiration date is always 180 days from the initial installation. The following query will give the expiration date of evaluation version:

-- Evaluation Version Expire Date
SELECT create_date AS InstallationDate,
DATEADD(DD, 180, create_date) AS 'Expiry Date'
FROM sys.server_principals
WHERE sid = 0x010100000000000512000000
GO

I believe there is a way to do this using registry, but I have not explored it personally. Now as what I’ve said earlier, there are many different blog posts on this subject. Let me list a few which I really enjoyed to read as they shared a few more insights about this subject:

Retrieving SQL Server 2012 Evaluation Period Expiry Date

How to find the Installation Date for an Evaluation Edition of SQL Server

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – SmallDateTime and Precision – A Continuous Confusion

Some kinds of confusion never go away. Here is one of the ancient confusing things in SQL. The precision of the SmallDateTime is one concept that confuses a lot of people, proven by the many messages I receive everyday relating to this subject.

Let me start with the question: What is the precision of the SMALLDATETIME datatypes?

What is your answer? Write it down on your notepad.

Now if you do not want to continue reading the blog post, head to my previous blog post over here: SQL SERVER – Precision of SMALLDATETIME.

A Social Media Question

Since the increase of social media conversations, I noticed that the amount of the comments I receive on this blog is a bit staggering. I receive lots of questions on facebooktwitter or Google+. One of the very interesting questions yesterday was asked on Facebook by Raghavendra. I am re-organizing his script and asking all of the questions he has asked me. Let us see if we could help him with his question:

CREATE TABLE #temp
(name VARCHAR(100),registered smalldatetime)
GO
DECLARE @test smalldatetime
SET @test=GETDATE()
INSERT INTO #temp
VALUES ('Value1',@test)
INSERT INTO #temp
VALUES ('Value2',@test)
GO
SELECT *
FROM #temp
ORDER BY registered DESC
GO
DROP TABLE #temp
GO

Now when the above script is ran, we will get the following result:

smalldt1 SQL SERVER   SmallDateTime and Precision   A Continuous Confusion

Well, the expectation of the query was to have the following result. The row which was inserted last was expected to return as first row in result set as the ORDER BY descending.

smalldt2 SQL SERVER   SmallDateTime and Precision   A Continuous Confusion

Side note: Because the requirement is to get the latest data, we can’t use any  column other than smalldatetime column in order by. If we use name column in the order by, we will get an incorrect result as it can be any name.

My Initial Reaction

My initial reaction was as follows:

1) DataType DateTime2: If file precision of the column is expected from the column which store date and time, it should not be smalldatetime. The precision of the column smalldatetime is One Minute (Read Here) for finer precision use DateTime or DateTime2 data type.

Here is the code which includes above suggestion:

CREATE TABLE #temp
(name VARCHAR(100), registered datetime2)
GO
DECLARE @test datetime2
SET @test=GETDATE()
INSERT INTO #temp
VALUES ('Value1',@test)
INSERT INTO #temp
VALUES ('Value2',@test)
GO
SELECT *
FROM #temp
ORDER BY registered DESC
GO
DROP TABLE #temp
GO

2) Tie Breaker Identity: There are always possibilities that two rows were inserted at the same time. In that case, you may need a tie breaker. If you have an increasing identity column, you can use that as a tie breaker as well.


CREATE TABLE #temp
(ID INT IDENTITY(1,1), name VARCHAR(100),registered datetime2)
GO
DECLARE @test datetime2
SET @test=GETDATE()
INSERT INTO #temp
VALUES ('Value1',@test)
INSERT INTO #temp
VALUES ('Value2',@test)
GO
SELECT *
FROM #temp
ORDER BY ID DESC
GO
DROP TABLE #temp
GO

Those two were the quick suggestions I provided. It is not necessary that you should use both advices. It is possible that one can use only DATETIME datatype or Identity column can have datatype of BIGINT or have another tie breaker.

An Alternate NO Solution

In the facebook thread this was also discussed as one of the solutions:

CREATE TABLE #temp
(name VARCHAR(100),registered smalldatetime)
GO
DECLARE @test smalldatetime
SET @test=GETDATE()
INSERT INTO #temp
VALUES ('Value1',@test)
INSERT INTO #temp
VALUES ('Value2',@test)
GO
SELECT name, registered,
ROW_NUMBER() OVER(ORDER BY registered DESC) AS "Row Number"
FROM #temp ORDER BY 3 DESC
GO
DROP TABLE #temp
GO

However, I believe it is not the solution and can be further misleading if used in a production server. Here is the example of why it is not a good solution:

CREATE TABLE #temp
(name VARCHAR(100) NOT NULL,registered smalldatetime)
GO
DECLARE @test smalldatetime
SET @test=GETDATE()
INSERT INTO #temp
VALUES ('Value1',@test)
INSERT INTO #temp
VALUES ('Value2',@test)
GO
-- Before Index
SELECT name, registered,
ROW_NUMBER() OVER(ORDER BY registered DESC) AS "Row Number"
FROM #temp ORDER BY 3 DESC
GO
-- Create Index
ALTER TABLE #temp
ADD CONSTRAINT [PK_#temp] PRIMARY KEY CLUSTERED
(name DESC)
GO
-- After Index
SELECT name, registered,
ROW_NUMBER() OVER(ORDER BY registered DESC) AS "Row Number"
FROM #temp ORDER BY 3 DESC
GO
DROP TABLE #temp
GO

smalldt3 SQL SERVER   SmallDateTime and Precision   A Continuous Confusion

Now let us examine the resultset. You will notice that an index which is created on the base table which is (indeed) schema change the table but can affect the resultset. As you can see, an index can change the resultset, so this method is not yet perfect to get the latest inserted resultset.

No Schema Change Requirement

After giving these two suggestions, I was waiting for the feedback of the asker. However, the requirement of the asker was there can’t be any schema change because the application was used by many other applications. I validated again, and of course, the requirement is no schema change at all. No addition of the column of change of datatypes of any other columns. There is no further help as well.

This is indeed an interesting question. I personally can’t think of any solution which I could provide him given the requirement of no schema change. Can you think of any other solution to this?

Need of Database Designer

This question once again brings up another ancient question:  “Do we need a database designer?” I often come across databases which are facing major performance problems or have redundant data. Normalization is often ignored when a database is built fast under a very tight deadline. Often I come across a database which has table with unnecessary columns and performance problems. While working as Developer Lead in my earlier jobs, I have seen developers adding columns to tables without anybody’s consent and retrieving them as SELECT *.  There is a lot to discuss on this subject in detail, but for now, let’s discuss the question first. Do you have any suggestions for the above question?

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Saturday Fun Puzzle with SQL Server DATETIME2 and CAST

Note: I have used SQL Server 2012 for this small fun experiment.

Here is what we are going to do. We will run the script one at time instead of running them all together and try to guess the answer. I am confident that many will get it correct but if you do not get correct, you learn something new.

Let us create database and sample table.

CREATE DATABASE DB2012
GO
USE DB2012
GO
CREATE TABLE TableDT
(DT1 VARCHAR(100), DT2 DATETIME2,
DT1C AS DT1, DT2C AS DT2);
INSERT INTO TableDT (DT1, DT2)
SELECT GETDATE(), GETDATE()
GO

There are four columns in the table. The first column DT1 is regular VARCHAR and second DT2 is DATETIME2. Both of the column are been populated with the same data as I have used the function GETDATE(). Now let us do the SELECT statement and get the result from both the columns.

Before running the query please guess the answer and write it down on the paper or notepad.

Question 1: Guess the resultset

SELECT DT1, DT2
FROM TableDT
GO

Now once again run the select statement on the same table but this time retrieve the computed columns only. Once again I suggest you write down the result on the notepad.

Question 2: Guess the resultset

SELECT DT1C, DT2C
FROM TableDT
GO

Now here is the best part. Let us use the CAST function over the computed columns. Here I do want you to stop and guess the answer for sure. If you have not done it so far, stop do it, believe me you will like it.

Question 3: Guess the resultset

SELECT CAST(DT1C AS DATETIME2) CDT1C,
CAST(DT2C AS DATETIME2) CDT1C
FROM TableDT
GO

Now let us inspect all the answers together and see how many of you got it correct.

Answer 1:

dt1 SQL SERVER   Saturday Fun Puzzle with SQL Server DATETIME2 and CAST

Answer 2:

dt2 SQL SERVER   Saturday Fun Puzzle with SQL Server DATETIME2 and CAST

Answer 3: 

dt3 SQL SERVER   Saturday Fun Puzzle with SQL Server DATETIME2 and CAST

If you have not tried to run the script so far, you can execute all the three of the above script together over here and see the result together.

SELECT CAST(DT1C AS DATETIME2) CDT1C,
CAST(DT2C AS DATETIME2) CDT1C
FROM TableDT
GO

ad4 SQL SERVER   Saturday Fun Puzzle with SQL Server DATETIME2 and CAST

Here is the Saturday Fun question to you – why do we get same result from both of the expressions in Question 3, where as in question 2 both the expression have different answer. I will publish the valid answer with explanation in future blog posts.

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Various Leap Year Logics

Earlier I wrote one article on Leap Year and created one video about Leap Year. My point of view was to demonstrate how we can use SQL Server 2012 features to identify Leap year. How ever during the conversation I had some really good conversation. Here are updates for those who have missed reading the excellent comments on the blog.

Incorrect Logic

There are so many people still think Leap Year is the event which is consistently happening at every four year and the way to find it is divide the year with 4 and if the remainder is 0. That year is leap year. Well, it is not correct.

Comment by David Bridge

Check out this excerpt from wikipedia page

http://en.wikipedia.org/wiki/Leap_year

“most years that are evenly divisible by 4 are leap years…”

“…Some exceptions to this rule are required since the duration of a solar year is slightly less than 365.25 days. Years that are evenly divisible by 100 are not leap years, unless they are also evenly divisible by 400, in which case they are leap years. For example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. Similarly, 2100, 2200, 2300, 2500, 2600, 2700, 2900 and 3000 will not be leap years, but 2400 and 2800 will be.”

If you use logic of divide by 4 and remainder is 0 to find leap year, you will may end up with inaccurate result. The correct way to identify the year is to figure out the days of February and if the count is 29, the year is for sure leap year.

Valid Alternate Solutions

Comment by sainswor99insworth

IIF((@Year%4=0 AND @Year%100 != 0) OR @Year%400=0, 1,0)

Comment by Madhivanan

Madhivanan has written a blog post about an year ago where he listed multiple ways to find leap year.

Comment by Jayan

DECLARE @year INT
SET
@year = 2012
IF (((@year % 4 = 0) AND (@year % 100 != 0)) OR (@year % 400 = 0))
PRINT ’1'
ELSE
print ’0'

Comment by David

DECLARE @Year INT = 2012
SELECT ISDATE('2/29/' + CAST(@Year AS CHAR(4)))

Comment by David Bridge

Incidentally – Another approach would be to take one day off March 1st and see if it is 29.

Reference: Pinal Dave (http://blog.sqlauthority.com)

SQL SERVER – Detecting Leap Year in T-SQL using SQL Server 2012 – IIF, EOMONTH and CONCAT Function

leap year SQL SERVER   Detecting Leap Year in T SQL using SQL Server 2012   IIF, EOMONTH and CONCAT Function

Note: Tomorrow is February 29th. This blog post is dedicated to coming tomorrow – a special day :)

Subu: “How can I find leap year in using SQL Server 2012?

Pinal: “Are you asking me how to year 2012 is leap year using T-SQL – search online and you will find many example of the same.”

Subu: “No. I am asking – How can I find leap year in using SQL Server 2012?

Pinal: “Oh so you are asking – How can I find leap year in using SQL Server 2012?

Subu: “Yeah – How can I find leap year in using SQL Server 2012?

Pinal: “Let me do that for you – How can you find leap year in using SQL Server 2012?

Indeed a fun conversation. Honestly, only reason I pasted our conversation here is – it was fun. What he was asking is that how to do it using new functions introduced in SQL Server 2012. Here is the article I have written which introduces all the new functions in SQL Server 2012 Summary of All the Analytic Functions – MSDN and SQLAuthority and 14 New Functions – A Quick Guide.

There are many functions written to figure out to figure out if any year is Leap Year or not. The same I have written using T-SQL function over here.

CREATE FUNCTION dbo.IsLeapYear (@year INT)
RETURNS INT
AS
BEGIN
RETURN
(IIF(DATEPART(dd,(EOMONTH(CONCAT(@year,'0201')))) = 29,1,0))
END
GO

What I really like is that I was able to use three newly introduced function in SQL Server 2012 in above script. You can read more about them here. IIF, EOMONTH and CONCAT.

You can validate above query by running following script.

SELECT dbo.IsLeapYear('2011') 'IsLeapYear';
SELECT dbo.IsLeapYear('2012') 'IsLeapYear';
GO

You will get result 1 if the year is leap year and 0 if year is not leap year.

Reference: Pinal Dave (http://blog.sqlauthority.com)