August 30, 2016

SQL Server Default Port

In this article, we are going to explore the default port number of SQL Server required for getting connected to different applications.

What is a Port? It is an endpoint of communication in an operating system. A port is always associated with an IP address of a host, and the protocol type of the communication, thereby completing the destination or origination address of a communication session. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number.
When front end applications want to connect to SQL Server, port number is essential.

The default port number of SQL Server is 1433.

How to get the port number in SQL Server?

Note - The steps are shown through SQL Server 2012 environment. They are largely applicable to SQL Server 2014 too.

Step 1: Open the SQL Server Configuration Manager window through Start > All Programs > Microsoft SQL Server 2012 > Configuration Tools 

sccm-navigation

Step 2: Explore SQL Native Client 11.0 Configuration (32bit)

sql-native-client-configuration

Step 3: Click on Client Protocols option within it  –

client-protocols

Step 4: Double click on TCP/IP from the right hand side pane

tcp-ip

We will get to know the Default Port as shown here

1433-default-port

The default port > 1433 port is the official Internet Assigned Number Authority (IANA) socket number for SQL Server. Client systems use TCP 1433 to connect to the database engine; SQL Server Management Studio (SSMS) uses the port to manage SQL Server instances across the network. You can reconfigure SQL Server to listen on a different port, but 1433 is by far the most common implementation.

Some other default SQL Server ports:

TCP 1434 – For Dedicated Admin Connection
UDP 1434 – For SQL Server Named Instance
TCP 2383 – For Default port of SSAS
TCP 2382 – For Named instances of SSAS
TCP 135 – For SSIS & T-SQL Debugger
TCP 80 and 443 – For SSRS
TCP 4022 – For Service Broker

other-default-ports

August 17, 2016

SQL Server Update statement with JOIN

In this article, we are specifically going to see a practical usage of the UPDATE statement in SQL Server when the condition is based on JOIN of another table.

Example:

CREATE TABLE EMP
       (EMPNO Integer Primary Key,
        ENAME Varchar(15),
        JOB Varchar(9),
        MGR Integer,
        HIREDATE datetime,
        SAL Integer,
        COMM Integer,
        DEPTNO Integer);
go
INSERT INTO EMP VALUES
        (7369, 'SMITH',  'CLERK',     7902, '12/17/80',
        800, NULL, 20);
INSERT INTO EMP VALUES
        (7499, 'ALLEN',  'SALESMAN',  7698,
        '5/20/81',1600,  300, 30);
INSERT INTO EMP VALUES
        (7521, 'WARD',   'SALESMAN',  7698,
        '5/22/81', 1250,  500, 30);
INSERT INTO EMP VALUES
        (7566, 'JONES',  'MANAGER',   7839,
        '4/2/81',  2975, NULL, 20);
INSERT INTO EMP VALUES
        (7654, 'MARTIN', 'SALESMAN',  7698,
        '9/28/81', 1250, 1400, 30);
INSERT INTO EMP VALUES
        (7698, 'BLAKE',  'MANAGER',   7839,
        '5/1/81',  2850, NULL, 30);
INSERT INTO EMP VALUES
        (7782, 'CLARK',  'MANAGER',   7839,
        '6/9/81',  2450, NULL, 10);
INSERT INTO EMP VALUES
        (7788, 'SCOTT',  'ANALYST',   7566,
        '12/9/82', 3000, NULL, 20);
INSERT INTO EMP VALUES
        (7839, 'KING',   'PRESIDENT', NULL,
        '11/17/81', 5000, NULL, 10);
INSERT INTO EMP VALUES
        (7844, 'TURNER', 'SALESMAN',  7698,
        '9/8/1981',  1500,    0, 30);
INSERT INTO EMP VALUES
        (7876, 'ADAMS',  'CLERK',     7788,
        '1/12/83', 1100, NULL, 20);
INSERT INTO EMP VALUES
        (7900, 'JAMES',  'CLERK',     7698,
        '12/3/81',   950, NULL, 30);
INSERT INTO EMP VALUES
        (7902, 'FORD',   'ANALYST',   7566,
        '12/3/81',  3000, NULL, 20);
INSERT INTO EMP VALUES
        (7934, 'MILLER', 'CLERK',     7782,
        '1/23/82', 1300, NULL, 10);
go

CREATE TABLE DEPT
       (DEPTNO INTEGER Primary Key,
        DNAME VARCHAR(14),
        LOC VARCHAR(13) );
go
INSERT INTO DEPT VALUES
        (10,'ACCOUNTING','NEW YORK');
INSERT INTO DEPT VALUES (20,'RESEARCH','DALLAS');
INSERT INTO DEPT VALUES
        (30,'SALES','CHICAGO');
INSERT INTO DEPT VALUES
        (40,'OPERATIONS','BOSTON');

Let us see the two tables.

select * from emp
go
select * from dept
go

emp-dept-table

Here we can see that this is a typical parent-child table relationship. Many a times, the end user wants to see the Employee Names (Enames) and Department Names (Dnames). But for that, they need to surrender to the inner join technique. Right now, only 14 rows are in emp table and 4 rows in dept.

But in a real time production environment, the number of records will be much higher. So this may result into a performance overhead. Therefore the DBA in such scenarios may decide to add the DName column in Emp table itself to eliminate the a JOIN overhead.

Note: Here we are moving towards an intentional De-Normalization technique.

The following ALTER Table command is used for that.

Alter Table Emp
Add Dname Varchar(40)

But now the problem is that for existing records if we see the DName colum, then it will be Null. Let us check it.

select * from emp

sql-adding-dname-column

So now we want to update each Dname as per the Dname of Dept table. For this we will issue the Update statement with join.

Update Emp 
set Dname  = Dept.DName
From Emp, Dept
where Emp.Deptno = Dept.Deptno

Technique: Here the update technique with join is used in the following sequential steps.

1. Every record of Emp is taken.
2. Its deptno is matched with deptno of Dept table.
3. The corresponding DName of Dept table is assigned to that row.
4. Next row of Emp is taken.
5. Step numbers 2 & 3 are repeated.
6. This process continues till the last row is reached by Emp table.

So now let us see the Emp table again.

select * from emp

after-update-with-sql-join

and that’s how we can use the Update statement with JOIN in SQL Server.

August 07, 2016

SQL Server Substring with CharIndex

In this article we are going to explore the T-SQL function CharIndex and also how to use it with another T-SQL function Substring().

CharIndex: This function returns the location of a substring in a string. By default, it is not case sensitive and is useful to check the position of a particular character or digit in the string. I have seen this function being used in product codes, different types of IDs for validation purpose, or to get some business understanding of that code/ID. Here’s the syntax:

CHARINDEX( Substring or Character, string, [start_position] )

where..

Substring or Character - The string that you want to find. It has to be within string data type family such as char or varchar only.
String - The string or number or an alphanumeric value to search within.
start_position - Optional. The position in string where the search will start. The first position is 1.

The function returns bigint if the expressionToSearch is of varchar(max), nvarchar(max), or varbinary(max) data types; otherwise, it retuns an int.

Substring with CharIndex examples:

select charindex('C','ABCDEF',1) 
-- Returns 3

select charindex('C','ABCDEF') 
-- Still returns 3 as start_position is option, default is 1

select charindex('c','ABCDEF',1) 
-- By default not case sensitive, so returns 3

select charindex('c','ABCDEF' COLLATE Latin1_General_CS_AS) 
–- Returns 0 as lowercase c is not found.

select charindex('Z','ABCDEF',1) 
-- Returns 0 as there is no Z character

select charindex('A','ABCDAEFG',2) 
-- Returns the second position of A, i.e. 5

select charindex('A','ABCDAEFG',9) 
-- Returns 0 as there is no ninth position there is no A

select charindex('4',123456) 
-- Searching from pure numbers, returns 4 as 4 is on fourth position

select charindex('curry','sqlservercurry.com') 
-- It considers the first character of string curry, 
-- i.e. c and then checks the first occurrence, so returns 10

Using CharIndex with Substring:

First let us check the functionality of the Substring function. It extracts a part of the string from the specified position.

Syntax:

Substring(String, Position or Index, Number of characters to extract)
select substring('abcdef', 2, 3) 
-- Returns bcd as 2 is from which position and 3 is number of characters to extract

Now the best usage of CharIndex with Substring is to create a functionality of “Text to Columns”.

That means many a times the names are in the format of “FirstName whitespace LastName” in the same column itself. In such cases, the need is to separate First Name in one column, and Last Name in another column for display purposes.

Consider the following example.

create table Authors
(AuthorID Varchar(2),
 AuthorName Varchar(60)
 )
 go
Insert into Authors Values('A1','Suprotim Agarwal')
Insert into Authors Values('A2','Mahesh Sabnis')
Insert into Authors Values('A3','Mandar Mulay')
go
select * from Authors
go

sql-default-author-table

Now let us say we want to display first name and last name in different columns. For that, we will use the substring function and within it, we will use CharIndex function to know the position number of white space.

See the following query:

select substring(AuthorName,1, charindex(' ',AuthorName)) as [First Name],
substring(AuthorName,(charindex(' ',AuthorName)) + 1, len(AuthorName)) as [Last Name]
from Authors
go

substring-with-charindex

Explanation:

First Name - substring(AuthorName,1, charindex(' ',AuthorName)) means from the first position till the first white space comes extract all the characters.

Last Name - substring(AuthorName,(charindex(' ',AuthorName)) + 1, len(AuthorName)) means to extract from the first white space + 1. Then to extract all remaining characters the len function is used.

And that’s how we use the SQL Server T-SQL Substring function, as well as Substring with CharIndex.

July 25, 2016

SQL Server Delete Duplicate Rows

There can be two types of duplication of rows in a table

1. Entire row getting duplicated because there is no primary key or unique key.
2. Only primary key or unique key value is different, but remaining all values are same.

Scenario 1: Delete duplicate rows without primary key or unique key.

Let us create the following example.

create table customers1
(CustId Int,
 CustName Varchar(20),
 CustCity Varchar(20),
 Passport_Number Varchar(20))
 go
Insert into customers1 Values(1, 'John', 'Paris', 'P123X78')
Insert into customers1 Values(2, 'Martin', 'London', 'L873X92')
Insert into customers1 Values(3, 'Smith', 'New York', 'N293Y99')
Insert into customers1 Values(1, 'John', 'Paris', 'P123X78')
go
select * from customers1
go

sql-row-duplicate

We want remove one of the duplicate records of John.

By issuing the following summary query, we can see which see which records are duplicate.

select * from customers1
Group by Custid,CustName, CustCity, Passport_Number
Having count(*) > 1

duplicate-row

Now we will add this row to a local temporary table.

Select * into #Temp_customers1 from customers1 where 1 = 2
Insert into #Temp_customers1
select * from customers1
Group by Custid,CustName, CustCity, Passport_Number
Having count(*) > 1

Now the situation is that the duplicate row is in the local temporary table. All we need to now is to delete records from main table customers1 as per matching custid of the local temporary table.

Delete from customers1
where custid in (select Custid from #Temp_customers1)

Will the above query work? Not entirely, as by using the above query, we lost all the duplicate records!! Let us see the table again.

select * from customers1
go

deleting-all-duplicate-rows

Now to keep one record of John, we will take help of the local temporary table again. Let us add the same record from temporary table into customers1 table.

Insert into Customers1
select * from #Temp_customers1
go

Finally we got a single record of John at the end. Let us confirm by seeing the Customers1 table.

select * from customers1
go

removing-duplicate-row

Once done, we can drop the local temporary table.

Scenario 2: Delete duplicate rows where primary key or unique key value is different but remaining values are same.

Let us create the following example.

create table customers2
(CustId Int Primary Key,
 CustName Varchar(20),
 CustCity Varchar(20),
 Passport_Number Varchar(20))
 go
Insert into customers2 Values(1, 'John', 'Paris', 'P123X78')
Insert into customers2 Values(2, 'Martin', 'London', 'L873X92')
Insert into customers2 Values(3, 'Smith', 'New York', 'N293Y99')
Insert into customers2 Values(4, 'John', 'Paris', 'P123X78')
Insert into customers2 Values(5, 'John', 'Paris', 'P123X78')
select * from customers2
go

Here is the same customer’s record, but this time John’s record has been added thrice with different customer ids but same Passport number!

duplicate-rows-different-custids

Scenario 2.a: Delete Duplicate rows but keep one using CTE

We need to use the technique of Self Join initially to check for duplicate records containing different custid but same passport number.

select distinct a.*
from customers2 a join customers2 b
on a.custid <> b.custid and a.CustName =  b.CustName
and a.CustCity = b.CustCity  and a.Passport_Number =  b.Passport_Number

selfjoin-showing-duplicate-rows


Now we have realized that custid 1, 4 & 5 are duplicate. The self-join statement accompanied by delete statement will give us the desired output of keeping the last duplicate record by eliminating all the previous duplicate records. We will use the Common Table Expression (CTE) and put the Self Join query in it.

With Duplicates as
(select distinct a.custid as Customer_ID
from customers2 a join customers2 b
on a.custid <> b.custid and a.CustName =  b.CustName
and a.CustCity = b.CustCity  and a.Passport_Number =  b.Passport_Number
) 
Delete from Customers2
where custid in (select Customer_ID from Duplicates)
and custid <> (select max(Customer_ID) from Duplicates)
Let’s check which rows got deleted.
select * from customers2
go

keeping-last-record

Scenario 2.b: Delete all duplicate records but keep the first original one

Let’s first truncate the customers2 table and add the same rows again.

Truncate Table customers2
go
Insert into customers2 Values(1, 'John', 'Paris', 'P123X78')
Insert into customers2 Values(2, 'Martin', 'London', 'L873X92')
Insert into customers2 Values(3, 'Smith', 'New York', 'N293Y99')
Insert into customers2 Values(4, 'John', 'Paris', 'P123X78')
Insert into customers2 Values(5, 'John', 'Paris', 'P123X78')
go

The only change in the sub query will be that we need to use min(CustomerID) instead of max(CustomerID).

So the query will be as follows.

With Duplicates as
(select distinct a.custid as Customer_ID
from customers2 a join customers2 b
on a.custid <> b.custid and a.CustName =  b.CustName
and a.CustCity = b.CustCity  and a.Passport_Number =  b.Passport_Number
) 
Delete from Customers2
where custid in (select Customer_ID from Duplicates)
and custid <> (select min(Customer_ID) from Duplicates)
Let us confirm this in the customers2 table.
select * from customers2
go

keeping-first-record


And that’s how we can delete duplicate records in SQL Server with tables without primary key, containing primary key and by keeping one original row.

July 17, 2016

T-SQL Insert Into Table Examples

In T-SQL, to add records into a table (SQL Server) we use a Data Manipulation Language (DML) command known as Insert statement. In this article, we are going to explore the different capabilities of the T-SQL Insert statement.

Let us create a table Table1 with 3 columns A, B and C

create table Table1
(A int,
 B Varchar(10),
 C Date)

Example 1: Add one complete row, date in American format

Here we will mention the actual column values in the Values clause in a sequence that matches the columns mentioned in the CREATE TABLE statement.

Syntax: Insert into Table_Name Values(Col1 Value, Col2 Value….., Coln Value)

Insert into Table1 Values (1,'Aa', '12/13/2014')

Example 2: Add one complete row, date in British format

The date can be entered either in American or British format.

Insert into Table1 Values (2,'Bb', '13-Dec-2014')

Example 3: Add one partial row, specifying Null
Sometimes we do not want to add values in every column. Let us create a new row by specifying values for A and C columns only.

Insert into Table1 Values (3, Null, '14-Dec-2014') 

Example 4: Add one partial row, specifying column names

Consider there are 25 columns in a SQL table, and we want to create a new row by specifying values for only 3 columns. In that case, mentioning Null for the remaining 22 columns multiple times will be cumbersome. So instead of that, we can only mention those 3 columns after the table name, and mention the values for only those 3 columns. The remaining 22 columns by default will get null values. Caution: There should not be primary key or NOT NULL constraint to any of those columns.

Syntax: Insert into Table_Name (Column1, Column3, Column5) Values(Col1 Value, Col3 Value, Col5 Value)

Insert into Table1(A,C) Values (4,'15-Dec-2014')

Note: The columns can be mentioned in any sequence after the table name, but then the values need to mentioned in the same sequence.

Example 5: Ignore the identity column while adding row.

If the table has identity (auto number generation property) column, then by default we cannot add value to that column.

Let us create table Table2 with A as identity column and B, C as integer data type columns

create table Table2
(A int identity,
 B int,
 C int)

To add a record, use the syntax demoed in Example 4.

Insert into Table2 (B,C) Values(100,200)

Example 6: Ignore the computed column while adding row

Let us create table Table3 with a,b and c as 3 columns. C will be the computed column.

create table Table3
(A int,
 B int,
 C as (a + b))
Insert into Table3 Values(200, 300)

The column C will implicitly get value 500!

Example 7: Bulk Insertion – Select along with Union All

If we want to add many records in a table through one statement, then SELECT statement can be associated with INSERT statement instead of values clause.

Let us create table Table4 first.

create table Table4
(a int, b varchar(10)
)

Now if we want add five rows in Table4, we will use SELECT statement along with UNION ALL.

Insert into Table4
Select 1,'A'
Union All
Select 2,'B'
Union All
Select 3,'C'
Union All
Select 4,'D'
Union All
Select 5,'E'

Example 8: Bulk Insertion – Select along with Union All, violation of constraint

If any record violates the constraint, then the entire set gets rejected.

create table Table5
(a int check (a <= 3), b varchar(10)
)
Insert into Table5
Select 1,'A'
Union All
Select 2,'B'
Union All
Select 3,'C'
Union All
Select 4,'D'
Union All
Select 5,'E'

No rows will get added in Table 5.

Example 9: Bulk Insertion – Multiple rows through Values clause itself

From SQL Server 2008 version onwards, the Values clause has been strengthen to add multiple rows.

Syntax:

Insert Into TableName
Values    (……………..),
           (……………..),
           (……………..),
           (……………..)

So in the Table4 now, we will add three records using the Values clause.

Insert into Table4
Values (6,'E'),(7,'F'),(8,'G')

Note: If any one record fails then the entire batch gets rejected.

Example 10: Bulk Insertion – Copying records of another table

Many a times we need to copy records from one table to another.

Insert into Target_Table
Select * from Source_Table

Note: Here it is assumed that the structure of source & target tables are same. That means the number of columns should be same, and positional columns should be compatible as per data type & size.
Let us create table Table6 similar to Table4

create table Table6
(a int, b varchar(10)
)

Now all records of Table4 need to be inserted in Table6.

Insert into Table6
Select * from Table4


Example 11: Bulk Insertion – Copying records of another table, but not in all columns.

Let us create table Table7 similar to Table4

create table Table7
(a int, b varchar(10)
)

Here we need to mention the column names. Suppose we want to add records, but taking values of column B only, then the command will be:

Insert into Table7(B)
Select B from Table4

Conclusion:


In this article we have seen how to add records into an SQL Server table using the T-SQL Insert statement with its multiple examples.

June 27, 2016

SQL Server Alter Table with Add Column

There are many scenarios where we need to do structural changes to a table, i.e. adding a column, modifying data type, dropping a column and so on. This change to an existing table is possible by issuing a SQL Server Data Definition Language (DDL) T-SQL command known as Alter Table.

In this article we are specifically focusing on adding a new column in a table using SQL Server Alter Table.

Scenario 1: Adding columns to empty table

When the table is created and if there are no records in that table, then there is no problem in adding a column or multiple columns to that table.

Let us see the following example:

create table customers1
(
  custid varchar(5),
 custname varchar(50)
)
go

Scenario 1.a: Adding single column:

After creating the table, we realize that date of birth (DOB) column needs to be added. The following command will help us in achieving this.

Alter Table customers1
Add DOB Date
go

Scenario 1.b: Adding multiple columns:

Adding two more columns is also very easy. Let us add nationality and gender as two more columns by just having a comma separator in each definition.

Alter Table customers1
Add Nationality Varchar(40), Gender Char(1)
go

Scenario 1.c: Adding columns with constraints:

Adding a column with constraint such as primary key, unique key, foreign key, not null, check or default is again not challenging in an empty table.

Note – A primary key constraint cannot be added on the new column if there is already a primary key on any other existing column.

Let us add SSN and deposit amount as two columns, SSN having primary key and deposit amount having check constraint.

Alter Table customers1
Add SSN Varchar(10) Primary Key, 
Deposit_Amount Integer Check(Deposit_Amount >= 200)
go

Scenario 2: Adding columns to table having records

When a column is added to a table with existing records, then for those records, by default a null value is assigned by SQL Server.

Adding column on table having existing records.

Let us create table customers2 and add 2 records in it.

create table customers2
(custid varchar(5),
 custname varchar(50)
 )
 Go
Insert into customers2 Values('C1','John')
Insert into customers2 Values('C2','Martin')
go

Scenario 2.a: Adding columns with default null values on existing records.

Alter Table customers2
Add DOB Date
go

Let us see the table Customers2

select * from customers2

sqlserver-nulls-new-column
Image2-No-Default-Value

Scenario 2.b: Adding columns with default value

It might happen that you want to add a column specifying some default value and there are existing records in the table. But in the default setup, those existing records will not get that value.
Let us add token amount as a column to this Customers2 table with default value as 100.

Alter Table customers2
Add Token_Amount Integer Default 100
go

Let us see the table Customers2

select * from customers2

sql-no-default-value
Image2-No-Default-Value

Note -The default value will be effective when new record is added.

Scenario 2.c: Adding columns with default value and applying those values on existing records.

Let us add another column tax with default value as 50. This value needs to be added to the existing records as well. We need to explicitly specify the clause With Values.


Alter Table customers2
Add Tax Integer Default 50 With Values
go

default-value-withclause
Image3-Default-Value-WithClause

Scenario 2.d: Adding columns with Not Null constraint on existing records.

Let us add a column Country with Not Null constraint. Now this will be contradictory because the earlier two records cannot have null value for Country.

Let us try.

Alter Table customers2
Add Country Varchar(50) Not Null
go

It will throw the following error.

ALTER TABLE only allows columns to be added that can contain nulls

To rectify this, we need to mention the default value which will safeguard the earlier records.

Scenario 2.e: Adding columns with not null constraint and default value on existing records

Let’s have India as the default value.

Alter Table customers2
Add Country Varchar(50) Default 'India' Not Null
go

Now this works fine. Let us see the table again.

select * from customers2

default-value-notnull
Image4-Default-Value-NotNull


Conclusion:

In this article, we have seen the following scenarios of using ALTER table to add column to a SQL Server table:

1. Adding one or multiple columns to an empty table.
2. Adding column to table having records. Those records get default value as null.
3. Adding column with default value to table having records
  • In absence of With Values clause
  • In presence of With Values clause
4. Adding column with not null constraint to table having records
  • In absence of Default clause
  • In presence of Default clause

June 18, 2016

SQL Server ISNULL() With Multi Column Names

Many a times we come across null values within tables in SQL Server. Null values are the values with no data; that means the data is missing or unknown. In this article, initially we will understand the SQL Server IsNull function, then we will move towards extending the IsNull functionality using Coalesce function.

Let us see the following example.

create table Identification
(empid Integer,
ename varchar(30) NOT NULL,
passport_number char(15) ,
license_number char(15) ,
pan char(15) ,
credit_card_number char(15) ,
account_number char(15) 
)
insert into identification values(1,'John',null,null,'PN-78654','CC-12345','AN-3456')
insert into identification values(2,'Martin','PS-566774',null,null,null,null)
insert into identification values(3,'Smith',null,null,null,null,null)
insert into identification values(4,'Roger',null,null,null,null,'AN-9876')
insert into identification values(5,'King',null,null,null,'CC-8787','AN-9878')
go
select * from identification
go

sql1-identification-table
Image1-Identification-Table

In the above table, every employee has an identity proof which is either a passport number, license number, pan, credit card or account number.

SQL Server ISNULL() Function Example

Syntax:
IsNull(Parameter1, Value if null)

IsNull function returns the first parameter if it’s not null. If the first parameter is null, then it returns the second parameter.

Suppose we want to see if an employee has a passport or not, here the IsNull function can help us.

See the following example of using SQL Server ISNULL in a Select Statement:

select empid, ename, IsNull(Passport_Number, 'Not Found') 
as 'Passport Status' from identification

sql2-isnull-with-single-column
Image2-IsNull-With-Single-Column

Limitation of IsNull() function:

IsNull function can check only if one value is null. It cannot check null for multiple values. That means it is not capable of handling the functionality of checking if the first parameter is null and then move on to check the next parameter for null.

Now assume that for report generation, we want to get the passport number or license number or pan number etc. for reference purpose. If passport number is null, then we need to extract the license number. If license number is null then pan, if pan is null then account number. If all are null then we need to flag a message ‘Invalid’.

The problem is that IsNull function here needs to be used in a nesting manner.

Let us see the ISNULL being used in a select statement in a nested fashion:

select empid, ename, 
IsNull(Passport_Number,IsNull(License_Number, 
IsNull(PAN, IsNull(Credit_Card_Number, IsNull(Account_Number,'Invalid'))))) 
as "Status"
from identification

sql3-isnull-multiple-columns
Image3-IsNull-Multiple-Columns

In the above select statement, we have used IsNull function 5 times to get the desired output.

ISNULL vs Coalesce Function:

There is an alternative way using another SQL Server function known as Coalesce.

Syntax of Coalesce:
COALESCE( parameter1, parameter2, parameter3,……. parameter_n , default_parameter)

Coalesce can take multiple parameters. It returns the first not null parameter. If all the parameters are null, then it will return the default parameter.

In other words, we can say that coalesce behaves as per the following syntax as well:

CASE
   WHEN (parameter1 IS NOT NULL) THEN expression1
   WHEN (parameter2  IS NOT NULL) THEN expression2
   ...
   ELSE expressionN
END

So instead of nesting IsNull function multiple times, we can use a single coalesce function and get the same output as shown here:

select empid, ename, 
Coalesce(Passport_Number,License_Number,PAN,Credit_Card_Number,Account_Number,'Invalid')
as "Using Coalesce" from identification

sql4-coalesce
Image4-Coalesce

Conclusion:

We have seen how the SQL Server IsNull function is suitable for checking one null value and how usage of coalesce function can eliminate the need of using IsNull function redundantly.

June 09, 2016

SQL Server T-SQL DateDiff Example

How do we find the difference between two dates in SQL Server. Not just the difference in the number of days, but also number of weeks, months.

The answer is by using DateDiff in SQL Server. Datediff is also suitable for getting the time elapsed between the start and end of a process.

Here are some real life examples of how t-sql datediff can be used to get a date difference:

1. Calculating the number of days remaining for a postpaid mobile service before it expires? Here an Automated system can calculate the date difference in sql and send an SMS to a customer informing him/her of the number of days remaining.

2. Particularly suitable in embedded systems to note the time taken for each process while manufacturing a product.

3. In library management automation to keep track of the number of days a book had been issued to a customer.

4. For daily login-logout required in an electronic attendance software system of any company. The tsql datediff function can be used to calculate the exact working hours of every employee.

The signature of this function is as follows:

DATEDIFF( interval, date1, date2 )

where date 1 & date 2 can be the actual date or a part of date like an year.

Note: date1 should be greater than or equal to date2.

Interval here can be any of the following as shown in the following chart:

t-sql-date-diff
image1-t-sql datediff interval

Let us see some examples to make it more clear and interesting.

select datediff (yy, '1984', '1997')  -- 13 years difference

select datediff (dd, '1984', '1986') -- 731 days difference

select datediff (mm, '1984', '1986') -- 24 months difference

select datediff (qq, '1984', '1986') -- 8 quarters difference

select datediff (hour,'2016/05/02 11:00', '2016/05/02 14:45' 
-- 3 hours difference

Database Oriented Example


The DateDiff SQL function can also be used in a where clause.

Let us create a sample database for the same in our SQL Server instance.

Use Master
go
create database DateDiff_Demo
go
Use DateDiff_Demo
go
create table Compaints_Details
(ComplaintID Integer Identity,
 CustId Varchar(7),
 Complaint_Description Varchar(100),
 Engineer_ID Varchar(4),
 Date_of_Complaint date,
 Date_of_Resolve date
 )
 Insert into Compaints_Details 
(CustiD, Complaint_Description, Engineer_ID, 
 Date_of_Complaint,Date_of_Resolve)
 Values
 ('C1', 'Modem problem', 'E1', '21-Apr-2016', '24-Apr-2016')

 Insert into Compaints_Details 
(CustiD, Complaint_Description, Engineer_ID, 
  Date_of_Complaint,Date_of_Resolve)
 Values
 ('C2', 'Wire Connection problem', 'E1', '22-Apr-2016', '22-Apr-2016')

 Insert into Compaints_Details 
 (CustiD, Complaint_Description, Engineer_ID, 
  Date_of_Complaint,Date_of_Resolve)
 Values
 ('C3', 'Socket problem', 'E1', '23-Apr-2016', '28-Apr-2016')

 Insert into Compaints_Details 
 (CustiD, Complaint_Description, Engineer_ID, 
  Date_of_Complaint,Date_of_Resolve)
 Values
 ('C5', 'LAN problem', 'E1', '29-Apr-2016', '29-Apr-2016')
 GO
 select* from Compaints_Details
 go

sql datediff sample data
Image2-SampleData to run a sql datediff query

Let us say we want to see how many days were elapsed for every complaint to get resolved.

Here we will use the Tsql DateDiff function.

SELECT  [ComplaintID]
      ,[CustId]
      ,[Complaint_Description]
      ,[Engineer_ID]
      ,[Date_of_Complaint]
      ,[Date_of_Resolve]
      , DateDiff(dd, [Date_of_Complaint]
      , [Date_of_Resolve]) as [Days taken to resolve]
FROM [DateDiff_Demo].[dbo].[Compaints_Details]

tsql datediff days
Image3-DaysTaken before a complaint was resolved

Conclusion:


And that’s how we can use the SQL Server T-SQL DateDiff function to calculate the day, month, year, and time part differences between two specified dates.

June 01, 2016

T-SQL Date Format with Convert

In this article we are going to see a very handy SQL Server T-SQL function for formatting date called Convert(). It is generally used to show date values in different styles or formats.

Normally any date value when entered in a SQL Server table gets displayed in the default format as YYYY-MM-DD. Many a times, in your client application you may need to change the output of date & time for display purpose. For doing this the T-SQL Convert function is used.


Convert Function Example

Let us create a sample database Convert_Demo in our SQL Server database instance.

Use Master
go
Create Database Convert_Demo
go
Use Convert_Demo
go
CREATE TABLE EMP
       (EMPNO Integer Primary Key,
        ENAME Varchar(15),
        JOB Varchar(9),
        MGR Integer,
        HIREDATE date,
        SAL Integer,
        COMM Integer,
        DEPTNO Integer);
go
INSERT INTO EMP VALUES
        (7369, 'SMITH',  'CLERK',     7902, '12/17/80',
        800, NULL, 20);
INSERT INTO EMP VALUES
        (7499, 'ALLEN',  'SALESMAN',  7698,
        '5/20/81',1600,  300, 30);
INSERT INTO EMP VALUES
        (7521, 'WARD',   'SALESMAN',  7698,
        '5/22/81', 1250,  500, 30);
INSERT INTO EMP VALUES
        (7566, 'JONES',  'MANAGER',   7839,
        '4/2/81',  2975, NULL, 20);
INSERT INTO EMP VALUES
        (7654, 'MARTIN', 'SALESMAN',  7698,
        '9/28/81', 1250, 1400, 30);
INSERT INTO EMP VALUES
        (7698, 'BLAKE',  'MANAGER',   7839,
        '5/1/81',  2850, NULL, 30);
INSERT INTO EMP VALUES
        (7782, 'CLARK',  'MANAGER',   7839,
        '6/9/81',  2450, NULL, 10);
INSERT INTO EMP VALUES
        (7788, 'SCOTT',  'ANALYST',   7566,
        '12/9/82', 3000, NULL, 20);
INSERT INTO EMP VALUES
        (7839, 'KING',   'PRESIDENT', NULL,
        '11/17/81', 5000, NULL, 10);
INSERT INTO EMP VALUES
        (7844, 'TURNER', 'SALESMAN',  7698,
        '9/8/1981',  1500,    0, 30);
INSERT INTO EMP VALUES
        (7876, 'ADAMS',  'CLERK',     7788,
        '1/12/83', 1100, NULL, 20);
INSERT INTO EMP VALUES
        (7900, 'JAMES',  'CLERK',     7698,
        '12/3/81',   950, NULL, 30);
INSERT INTO EMP VALUES
        (7902, 'FORD',   'ANALYST',   7566,
        '12/3/81',  3000, NULL, 20);
INSERT INTO EMP VALUES
        (7934, 'MILLER', 'CLERK',     7782,
        '1/23/82', 1300, NULL, 10);
go

Now let us see the default presentation style of the hiredate column by executing the following SQL statement.

select ename, hiredate from emp

sql-default-date-format


Image1-Default-date-format


Syntax of Convert function

CONVERT(data_type(length),data_to_be_converted,style)

Data_type(length) - varchar data type particulary for displaying dates in different format.

data_to_be_converted - The date value which needs to be converted.

Style - There are some predefined style ids like 101 for American date format, 103 in British format and so on. The style chart has been shown next –

sql-date-formats

Now let us see the employee names & hiredate in American as well as British formats using T-SQL Convert function.

select ename, hiredate as [Default Date Format],
convert(varchar, hiredate, 101) as [American],
convert(varchar, hiredate, 103) as [British] 
from emp

sql-changed-date-formats
Image2-Changed-Date-Formats


Convert without StyleID:

Convert is also useful to convert from one data type to another – For example changing Float to Int, Number to Float or Number to Varchar.

Using Convert to change from Float to Int


SELECT CONVERT(int, 14.85)

sql-changing-float-to-int


Image3-Changing-Float-To-Int

Using Convert to change from Number to Float


SELECT CONVERT(float, 14.0989654)    

sql-number-to-float
Image4-Number-to-Float

Using Convert to change from Number to Varchar

SELECT CONVERT(varchar(4), '12.3456')

sql-number-to-varchar
Image5-Number-to-Varchar

Conclusion:

 
We have seen in this article that using T-SQL function Convert, we can display date in different formats and also can type cast one data type into another.

May 15, 2016

Nested Case Statement in SQL Server

This article is a continuation of SQL Server CASE Statement and CASE WHEN Examples . Today we will learn about Nested Case Statement in SQL Server.

We can nest CASE statements similar to nested ifs that we find in most programming languages.

Let us see an example.

select ename, job, sal, case  -- Outer Case
    when ename like 'A%' then
    case when sal >= 1500 then 'A' -- Nested Case
    end
    when ename like 'J%' then
    case when sal >= 2900 then 'J' -- Nested Case
    end
end as "Name-Grade"            
From Emp

7-nested-case
Image 7-Nested-Case

Limit of nesting a CASE function is up to 10 levels only.

In the following example, the limit of 10 is completely utilized.

Declare @x int
set @x = 1
Select 
case when @x <= 100 then  -- Level 1
 case when @x <= 90 then -- Level 2
    case when @x <= 80 then -- Level 3
        case when @x <= 70 then -- Level 4
            case when @x <= 60 then -- Level 5
                case when @x <= 50 then -- Level 6
                    case when @x <= 40 then -- Level 7
                       case when @x <= 30 then --Level 8
                         case when @x <= 20 then--Level 9
                           case when @x<= 10 then--Level 10
                                100
End End End End End End End End End 
End as "Nested Case" 
--Ending all levels!

8-nested-case-upto-10-levels
Image 8-Nested-Case-Upto-10-Levels

If nesting is exceeding 10 levels, then SQL Server throws an error.
Declare @x int
set @x = 1
Select 
case when @x <= 100 then  -- Level 1
case when @x <= 90 then -- Level 2
case when @x <= 80 then -- Level 3
    case when @x <= 70 then -- Level 4
        case when @x <= 60 then -- Level 5
            case when @x <= 50 then -- Level 6
                case when @x <= 40 then -- Level 7
                   case when @x <= 30 then --Level 8
                     case when @x <= 20 then--Level 9
                       case when @x<= 10 then--Level 10
                          case when @x <= 11 then -- 11
                             100
End End End End End End End End End End 
End as "Nested Case"

Msg 125, Level 15, State 4, Line 14
Case expressions may only be nested to level 10.