Sometimes most records under a certain column may hold the same value although just a few would be different. For example, if a school is using a database to register its students, all of them are more likely to be from the same state. In such a case, you can assist the user by automatically providing a value for that column. The user would then simply accept the value and change it only in the rare cases where the value happen to be different. To assist the user with this common value, you create what is referred to as a default value.

You can create a default value of a column when creating a table. To specify the default value of a column, in the top section, click the column. In the bottom section, click Default Value or Binding, type the desired value following the rules of the column's data type:

It the Data Type is	Intructions
Text-based (char, varchar, text, and their variants)	Enter the value in single-quotes
Numeric-based	Enter the value as a number but following the rules of the data type. For example, if you enter a value higher than 255 for a tinyint, you would receive an error
Date or Time	Enter the date as either MM/DD/YYYY or YYYY/MM/DD. You can optionally include the date in single-quotes. Enter the time following the rules set in the Control Panel (Regional Settings).
Bit	Enter the value as 0 for FALSE or any other long integer value for TRUE

To specify the default value in a SQL statement, when creating the column, before the semi-colon or the closing parenthesis of the last column, assign the desired value to the DEFAULT keyword. Here are examples:

CREATE TABLE Employees
(
    FullName VARCHAR(50),
    Address VARCHAR(80),
    City VARCHAR(40),
    State VARCHAR(40) DEFAULT = 'NSW',
    PostalCode VARCHAR(4) DEFAULT = '2000',
    Country VARCHAR(20) DEFAULT = 'Australia'
);
GO

After creating the table, the user does not have to provide a value for a column that has a default. If the user does not provide the value, the default would be used when the record is saved.

If the user provides a value for a column that has a default value and then deletes the value, the default value rule would not apply anymore: The field would simply become empty

One of the goals of a good table is to be able to uniquely identity each record. In most cases, the database engine should not confuse two records. Consider the following table:

Imagine that you want to change the value of an item named Long-sleeve jersey dress. Because you must find the item programmatically, you can start looking for an item with that name. This table happens to have two items with that name. You may then decide to look for an item using its category. In the Category column, there are too many items named Women. In the same way, there are too many records that have a Large value in the Size column, same thing problem in the Unit Price column. This means that you don't have a good criterion you can use to isolate the record whose Item Name is Long-sleeve shirt.

To solve the problem of uniquely identifying a record, you can create a particular column whose main purpose is to distinguish one record from another. To assist you with this, the SQL allows you to create a column whose data type is an integer type but the user doesn't have to enter data for that column. A value would automatically be entered into the field when a new record is created. This type of column is called an identity column.

You cannot create an identity column one an existing table, only on a new table.

To create an identity column, if you are visually working in the design view of the table, in the top section, specify the name of the column. By tradition, the name of this column resembles that of the table but in singular. Also, by habit, the name of the column ends with _id, Id, or ID.

After specifying the name of the column, set its data type to an integer-based type. Usually, the data type used is int. In the bottom section, click and expand the Identity Specification property. The first action you should take is to set its (Is Identity) property from No to Yes.

Once you have set the value of the (Is Identity) property to Yes, the first time the user performs data entry, the value of the first record would be set to 1. This characteristic is controlled by the Identity Seed property. If you want the count to start to a value other than 1, specify it on this property.

After the (Is Identity) property has been set to Yes, the SQL interpreter would increment the value of each new record by 1, which is the default. This means that the first record would have a value of 1, the second would have a value of 2, and so on. This aspect is controlled by the Identity Increment property. If you want to increment by more than that, you can change the value of the Identity Increment property.

1. In the Object Explorer, under WorldStatistics, right-click Tables and click New Table...
2. Set the name of the column to ContinentID and press Tab
3. Set its data type to int and press F6.
   In the lower section of the table, expand Identity Specification and double-click (Is Identity) to set its value to Yes
4. Complete the table as follows:
    

   Column Name	Data Type	Allow Nulls
   ContinentID
   Continent	varchar(80)	Unchecked
   Area	bigint
   Population	bigint

5. Save the table as Continents

If you are programmatically creating a column, to indicate that it would be used as an identity column after its name and data type, type identity followed by parentheses. Between the parentheses, enter the seed value, followed by a comma, followed by the increment value. Here is an example:

CREATE TABLE StoreItems(
ItemID int IDENTITY(1, 1) NOT NULL, 
Category varchar(50),
[Item Name] varchar(100) NOT NULL,
Size varchar(20),
[Unit Price] money);
GO

CREATE TABLE RepairOrders
(
  RepairID int Identity(1,1) NOT NULL,
  CustomerName varchar(50),
  CustomerPhone varchar(20),
  RepairDate DateTime
);
GO

INSERT INTO RepairOrders(CustomerName, CustomerPhone, RepairDate)
	    VALUES('Annette Berceau', '301-988-4615', GETDATE());
GO
INSERT INTO RepairOrders(CustomerPhone, CustomerName, RepairDate)
	    VALUES('(240) 601-3795', 'Paulino Santiago', GETDATE());
GO
INSERT INTO RepairOrders(CustomerName, RepairDate, CustomerPhone)
	    VALUES('Alicia Katts', GETDATE(), '(301) 527-3095');
GO
INSERT INTO RepairOrders(RepairDate, CustomerPhone, CustomerName)
	    VALUES(GETDATE(), '703-927-4002', 'Bertrand Nguyen');
GO

There are various ways you can assist the user with data entry. Besides using a function, you can create an expression using operators such as those we reviewed in lessons 3 and 5. You can create an expression when creating a table, whether in the Table window or using SQL in a query window.

To create an expression when visually creating a table, in the top section, specify the column's name (only the column name is important). In the bottom section, expand the Computed Column Specification field and, in its (Formula) field, enter the desired expression. Here is an example:

You can also create an expression in SQL expression you are using to create a table. To do this, in the placeholder of the column, enter the name of the column, followed by AS, and followed by the desired expression. Here is an example:

CREATE TABLE Circle
(
    CircleID int identity(1,1) NOT NULL,
    Radius decimal(8, 3) NOT NULL,
    Area AS Radius *Radius * PI()
);
GO

When performing data entry, you must not provide a value for a column that has an expression; the SQL interpreter would provide the value automatically. Here is an example of entering data for the above Circle table:

INSERT INTO Circle(Radius) VALUES(46.82);
GO
INSERT INTO Circle(Radius) VALUES(8.15);
GO
INSERT INTO Circle(Radius) VALUES(122.57);
GO

When performing data entry, in some columns, even after indicating the types of values you expect the user to provide for a certain column, you may want to restrict a range of values that are allowed. To assist you with checking whether a newly entered value fits the desired range, Transact-SQL provides what is referred to as a check constraint.

A check constraint is a Boolean operation performed by the SQL interpreter. The interpreter examines a value that has just been provided for a column. If the value is appropriate:

1. The constraint produces TRUE
2. The value gets accepted
3. The value is assigned to the column

If the value is not appropriate:

1. The constraint produces FALSE
2. The value gets rejected
3. The value is not assigned to the column

You create a check constraint at the time you are creating a table.

To create a check constraint, when creating a table, right-click anywhere in (even outside) the table and click Check Constraints...

This would open the Check Constraints dialog box. From that window, you can click Add. Because a constraint is an object, you must provide a name for it. The most important piece of information that a check constraint should hold is the mechanism it would use to check its values. This is provided as an expression. Therefore, to create a constraint, you can click Expression and click its ellipsis button. This would open the Check Constraint Expression dialog box.

To create the expression, first type the name of the column on which the constraint will apply, followed by parentheses. In the parentheses, use the arithmetic and/or SQL operators we studied already. Here is an example that will check that a new value specified for the Student Number is greater than 1000:

After creating the expression, you can click OK. If the expression is invalid, you would receive an error and given the opportunity to correct it.

You can create as many check constraints as you judge necessary for your table:

After creating the check constraints, you can click OK.

To create a check constraint in SQL, first create the column on which the constraint will apply. Before the closing parenthesis of the table definition, use the following formula:

CONSTRAINT name CHECK (expression) 

The CONSTRAINT and the CHECK keywords are required. As an object, make sure you provide a name for it. Inside the parentheses that follow the CHECK operator, enter the expression that will be applied. Here is an example that will make sure that the hourly salary specified for an employee is greater than 12.50:

CREATE TABLE Employees
(
	[Employee Number] nchar(7),
	[Full Name] varchar(80),
	[Hourly Salary] smallmoney,
	CONSTRAINT CK_HourlySalary CHECK ([Hourly Salary] > 12.50)
);

It is important to understand that a check constraint it neither an expression nor a function. A check constraint contains an expression and may contain a function as part of its definition.

After creating the constraint(s) for a table, in the Object Explorer of Microsoft SQL Server Management Studio, inside the table's node, there is a node named Constraints and, if you expand it, you would see the name of the constraint.

With the constraint(s) in place, during data entry, if the user (or your code) provides an invalid value, an error would display. Here is an example:

Instead of an expression that uses only the regular operators, you can use a function to assist in the checking process. You can create and use your own function or you can use one of the built-in Transact-SQL functions.

This property allows you to specify that a column with the Identity property set to Yes is used as a ROWGUID column.

Because different languages use different mechanisms in their alphabetic characters, this can affect the way some sort algorithms or queries are performed on data, you can ask the database to apply a certain language mechanism to the field by changing the Collation property. Otherwise, you should accept the default specified by the table.

Another technique used to get data into one or more tables consists of importing already existing data from another database or from any other recognizable data file. Microsoft SQL Server provides various techniques and means of importing data.

The easiest type of data that can be imported into SQL Server, and which is available on almost all database environments, is the text file. Almost every database environment allows you to import a text file but data from that file must be formatted appropriately. For example, the information stored in the file must define the columns as distinguishable by a character that serves as a separator. This separator can be the single-quote, the double-quote, or any valid character. Data between the quotes is considered as belonging to a distinct field. Besides this information, the database would need to separate information from two different columns. Again, a valid character must be used. Most databases, including Microsoft SQL Server, recognize the comma as such a character. The last piece of information the file must provide is to distinguish each record from another. This is easily taken car of by the end of line of a record. This is also recognized as the carriage return.

These directives can help you manually create a text file that can be imported into Microsoft SQL Server. In practicality, if you want to import data that resides on another database, you can ask that application to create the source of data. Most applications can do that and format the data. That is the case for the data we will use in the next exercise: it is data that resided on a Microsoft Access database and was prepared to be imported in Microsoft SQL Server.

After importing data, you should verify and possibly format it to customize its fields.

1. Download the Students text file and save it to your hard drive
2. In the SQL Server Management Studio, right-click the Databases node and click New Database...
3. Type ROSH and press Enter
4. In the Object Explorer, right-click ROSH, position the mouse on Tasks and click Import Data
5. On the first page of the wizard, click Next
6. On the second page, click the arrow of the Data Source combo box and select Flat File Source
7. On the right side of File Name, click the Browse button
8. Locate and select the Students.txt file you had saved
    
   
9. Under Data Source, click Advanced
10. As Column is selected, in the right list, click Name and type StudentID
11. In the middle list, click each column and change its Name in the right column as follows:
     

    Column	Name
    Column0	StudentID
    Column1	FirstName
    Column2	LastName
    Column3	DateOfBirth
    Column4	Gender
    Column5	Address
    Column6	City
    Column7	State
    Column8	ZIPCode
    Column9	HomePhone
    Column10	EmailAddress
    Column11	ParentsNames
    Column12	SPHome
    Column13	EmrgName
    Column14	EmrgPhone

     
    
12. To see the list of columns, under Data Source, click Columns
     
    
13. Click Next 4 times
14. Click Finish
     
    
15. Click Close
16. Back in the Object Explorer, expand the ROSH and its Tables nodes.
    Right-click Students and click Design
17. As the StudentID field is selected, press Tab and change its data type to int
18. Press F6 and expand Identity Specification. Double-click (Is Identity) to set its value to Yes
19. Change the other columns as follows:
     
    
20. To save the table, click the Save button on the Standard toolbar:
     
    
21. When a Validation Warnings dialog box presents a few warnings, click Yes
22. Close the table
23. To view data stored on the table, in the Object Explorer, right-click dbo.Students and click Open Table

One of the simplest operations a user can perform on a table consists of looking for a record. To do this, the user would open the table that contains the records and visually check them, looking for a piece of information, such as a student's last name.

As the database developer, you too can look for a record and there are various techniques you can use. To assist you with this, Transact-SQL provides a function named EXISTS. Its syntax is:

BIT EXISTS(SELECT Something)

This function takes one argument. The argument must be a SELECT statement that would be used to get the value whose existence would be checked. For example, in Lesson 2, we mentioned a system database names databases that contains a record of all databases stored on your server. You can use the EXISTS() function to check the existence of a certain database. The formula you would use is:

IF EXISTS (
   SELECT name 
   FROM sys.databases 
   WHERE name = N'DatabaseName'
)

In the DatabaseName placeholder, you can enter the name of the database.

Before visually performing some operations on a table, you must first select one or more records. In the Table window, to select one record, position the mouse on the left button of the record and click:

To select a range of records, click the gray button of one of the records, press and hold Shift, then click the gray button of the record at the other extreme.

To select the records in a random fashion, select one record, press and hold Ctrl, then click the gray button of each desired record:

To select all records of a table, click the gray button on the left of the first column:

To visually modify one or more records on a table, first open it (you right-click the table in the Object Explorer and click Open Table) to view its records. Locate the record and the field you want to work on and perform the desired operation.

Record maintenance includes viewing records, looking for one or more records, modifying one or more records, or deleting one or more records.

Updating a record consists of changing its value for a particular column. To update a record using SQL:

• In the Object Explorer, you can right the table, position the mouse on Script Table As -> UPDATE To -> New Query Editor Window
• Open an empty query window and type your code

To support record maintenance operations, the SQL provides the UPDATE keyword that is used to specify the table on which you want to maintain the record(s). The basic formula to use is:

UPDATE TableName
SET ColumnName = Expression

With this formula, you must specify the name of the involved table as the TableName factor of our formula. The SET statement allows you to specify a new value, Expression, for the field under the ColumnName column.

Consider the following code to create a new database named VideoCollection and to add a table named Videos to it:

CREATE DATABASE VideoCollection;
GO
USE VideoCollection;
GO
CREATE TABLE Videos (
  VideoID INT NOT NULL IDENTITY(1,1),
  VideoTitle varchar(120) NOT NULL,
  Director varchar(100) NULL,
  YearReleased SMALLINT,
  VideoLength varchar(30) NULL,
  Rating varchar(6)
);
GO
INSERT INTO Videos(VideoTitle, Director, YearReleased, VideoLength)
VALUES('A Few Good Men','Rob Reiner',1992,'138 Minutes');

INSERT INTO Videos(VideoTitle, Director, YearReleased, VideoLength)
VALUES('The Silence of the Lambs','Jonathan Demme',1991,'118 Minutes');

INSERT INTO Videos(VideoTitle, Director, VideoLength)
VALUES('The Distinguished Gentleman', 'James Groeling', '112 Minutes');

INSERT INTO Videos(VideoTitle, Director, VideoLength)
VALUES('The Lady Killers', 'Joel Coen & Ethan Coen', '104 Minutes');

INSERT INTO Videos(VideoTitle, Director, VideoLength)
VALUES('Ghosts of Mississippi', 'Rob Reiner', '130 Minutes');
GO

Imagine that, at one time, on a particular table, all records need to receive a new value under one particular column or certain columns. There is no particular way to visually update all records of a table. You can just open the table to view its records, and then change them one at a time.

In SQL, the primary formula of the UPDATE statement as introduced on our formula can be used to update all records. Here is an example:

USE VideoCollection;
GO
UPDATE Videos
SET Rating = 'R';
GO

With this code, all records of the Videos table will have their Rating fields set to a value of R:

Editing a record consists of changing a value in a field. It could be that the field is empty, such as the © Year of the the 'The Lady Killers' video of the following table. It could be that the value is wrong, such as the Director of the the 'The Distinguished Gentleman' video of this table:

To edit a record, first open the table to view its records. Locate the record, the column on which you want to work, and locate the value you want to change, then change it.

In SQL, you must provide a way for the interpreter to locate the record. To do this, you would associate the WHERE operator in an UPDATE statement using the following formula:

UPDATE TableName
SET ColumnName = Expression
WHERE Condition(s)

The WHERE operator allows you to specify how the particular record involved would be identified. It is  very important, in most cases, that the criterion used be able to uniquely identify the record. In the above table, imagine that you ask the interpreter to change the released year to 1996 where the director of the video is Rob Reiner. The UPDATE statement would be written as follows:

UPDATE Videos
SET YearReleased = 1996
WHERE Director = 'Rob Reiner';

In the above table, there are at least two videos directed by Rob Reiner. When this statement is executed, all video records whose director is Rob Reiner would be changed, which would compromise existing records that didn't need this change. This is where the identity column becomes valuable. We saw earlier that, when using it with the IDENTITY feature, the interpreter appends a unique value to each record. You can then use that value to identify a particular record because you are certain the value is unique.

Here is an example used to specify the missing copyright year of a particular record:

UPDATE Videos
SET YearReleased = 1996
WHERE VideoID = 5;
GO

Here is an example used to change the name of the director of a particular video:

UPDATE Videos
SET Director = 'Jonathan Lynn'
WHERE VideoTitle = 'The Distinguished Gentleman';

If you think all records of a particular table are, or have become, useless, you can clear the whole table, which would still keep its structure. To delete all records from a table, first select all of them, and press Delete. You would receive a warning:

If you still want to delete the records, click Yes. If you change your mind, click No.

Using SQL, to clear a table of all records, use the DELETE operator with the following formula:

DELETE TableName;

When this statement is executed, all records from the TableName factor would be removed from the table. Be careful when doing this because once the records have been deleted, you cannot get them back.

If you find out that a record is not necessary, not anymore, or is misplaced, you can remove it from a table. To remove a record from a table, you can right-click its gray box and click Delete. You can also first select the record and press Delete. You would receive a warning to confirm your intention.

To delete a record using SQL:

• In the Object Explorer, you can right the table, position the mouse on Script Table As -> DELETE To -> New Query Editor Window
• Open an empty query window and type your code

In SQL, to delete a record, use the DELETE FROM statement associate the WHERE operator. The formula to follow is:

DELETE FROM TableName
WHERE Condition(s)

The TableName factor is used to identify a table whose record(s) would be removed.

The Condition(s) factor allows you to identify a record or a group of records that carries a criterion. Once again, make sure you are precise in your criteria so you would not delete the wrong record(s).

Here is an example used to remove a particular record from the table:

DELETE FROM Videos
WHERE VideoTitle = 'The Lady Killers';

Here is an example used to clear the table of all videos:

DELETE FROM Videos;