MS Sql Server: Manipulating Database
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To manipulate a database, you can: 1) Add, modify, or delete fields using ALTER TABLE commands like ADD, ALTER COLUMN, and DROP COLUMN. 2) Add new records by inserting rows and delete existing records using a DELETE FROM table WHERE condition statement. 3) Take care with data type conversions when modifying fields to ensure compatibility.
MS Sql Server: Manipulating Database
- 1. 4SQL SERVER: MANIPULATING A DATABASE
- 2. Manipulating a DatabaseHOW TO MAKE CHANGES TO THE STRUCTURE OF THE DATABASE?A Database table can be defined by:The Fields(Columns) and their propertiesRecords(Rows) and their propertiesIt is important to understand clearly that the records are user-entries into a database table. Fields are created during the design phase of a databaseNow let us see how to carry out the changes to the above defined properties of a database.
- 3. Modifying the ColumnsThe Columns or fields in a database table can be easily modified using the ‘alter table’ command, which comes under DDL(Data Definition Language)What are the changes that can be made to a field?Add a new filed
- 4. Edit an existing field
- 5. Remove a field from table
- 6. Add a constraint on the data that a field can hold (will be dealt with later)Now lets see how these actions can be performed in SQL Server 2008
- 7. Add a new fieldThe SQL DDL command ‘alter table…add’ is used for adding a new fieldalter table <tableName> add <field name> <field type>;For example, consider the following animal database used by ‘MetaZooa’ Zoo, for maintaining the details of the animals in the zoo.
- 8. Add a new fieldNow, suppose the MetaZooa corp. decides to construct another Zoo beside the old one and divide the animals between the zoos. Then, the database of MetaZooa must contain details of the zoo-number also.
- 9. Add a new fieldSteps to add a new fieldConsidering the previous example, the command will be:alter table MetaZooDBaddZoo int;Run this command using ‘Go’ command.
- 10. Modifying an existing fieldNow, suppose MetaZooa decides to that ‘Zoo’ contains the Zoo Name rather than the number ‘1’ or ‘2’, we need to modify the field type.The Command is:alter table MetaZooDBalter column Zoo varchar(15);Run this command using ‘Go’ command.But we might have complications…
- 11. Modifying an existing fieldProblem:The Data contained in the field that is to be modified must be compatible with the destination data-type. Other-wise, conversion cannot be carried outCompatibility ChartSourceDestinationSourceVarchar(Strings)Integers (Int)Varchar (Strings)Integers (Int)Legend:Conversion Allowed:Conversion NOT allowed:Decimals (Float)Date and Time
- 12. Modifying an existing fieldSourceDestinationSourceVarchar (Strings)Decimals (Float)Date and TimeIntegers (Int)Decimals (Float)Date and Time
- 13. Remove a column from tableThe DDL command ‘alter table’ in conjunction with the ‘drop column’ is used to delete a column/field from a user table. The Syntax is:alter table <table_name> drop column <column_name>For example, consider the follwingDreamTable. Suppose the User wishes to remove the DreamType field… alter table DreamTable drop column DreamType
- 14. Deleting a RowA Record is a row in a table. For example, consider a fish database maintained by a ‘Eden-Lake Ecology farm’. Now, suppose the people go on a shark-mania and the sharp population vanished from the lake, it is meaningful for the Eco farm to remove its entry from the database.Now let us see the command
- 15. Deleting a RowDeleting a row:For deleting a row, it must be identified using a ‘distinguishing’ attribute which lets the computer tell it apart from other records.For the above example, the record can be identified using:The Primary key (FishID)Or any other special attribute (like Fish Name).But in general, always use the Primary Key, as it is best suited for uniquely identifying a record in a database table.NOTE: Strings/Date data-types must be encapsulated within single quotesdelete from <table_name> where <condition>delete from EdenFishTable where FishID = ‘23H’
- 16. Summary4. Manipulating a Database Adding Fields
- 17. Alter table… add
- 18. Modifying Fields
- 20. Deleting Fields
- 22. Removing Rows
- 23. Delete from..whereVisit more self help tutorialsPick a tutorial of your choice and browse through it at your own pace.The tutorials section is free, self-guiding and will not involve any additional support.Visit us at www.dataminingtools.net