SQL Server Basics

1. Full Backup: This is the most common and simplest back up method, It contains all the data in a specific database and enough log that is required to recover the database. It is the base of both differential back up and transaction log back up. 2. Differential Backup: It depend on the latest full backup of data. It contains all the changes that have been made since the last full backup of dat a.  3. Transaction Log Backup: The transaction log is a record of  all the transactions that have been performed against the database since the last transaction log backup. That means it includes all log records that were not backed up in the last transaction log. With transaction log backup you can recover the database to a specific point of time. This SQL Server backup type is possible only with full or bulk-logged recovery model. 4. File and File group Backup: This backup type allows you to backup one or more database file or file groups.  5.Parti...

 A trigger is a spacial type of stored procedure which is created on a particular table and it gets executed  in response to certain events (insert, update, delete) on that table. It is a database object which is bound to a table. You can not invoke it explicitly. SQL Server engine executes it implicitly when an event occurs on that table. In SQL server there are two types of triggers. 1. After Trigger (For Trigger) 2. Instead of Trigger After Trigger After trigger is also called as For trigger. It gets fired after an insert or delete or update on a table. Example: After a new employee record is inserted in employee table you want to insert a record in your Audit table saying "A new employee with name XYZ is added at 8 Aug 2017 5:17 PM". Before demonstrating this, let me explain about Magic tables. Magic tables in SQL Server: -Magic tables are temporary tables created by SQL server internally every time when a DML action is performed on a table wi...

DELETE DELETE removes some specific rows (with WHERE clause) or all rows (without WHERE clause) The operation can be rolled back.    DELETE is a DML command. This operation cause all DELETE triggers on table to fire. Conditions like WHERE clause can be used. Note: when we issue a DELETE command then all data get copied into ROLLBACK Tablespace first. Then delete operation get performed. That is why when you type ROLLBACK after deleting table, you can get back the data (The system get it for you from the Rollback Tablespace) TRUNCATE TRUNCATE removes all rows from a table. The operation cannot be rolled back. TRUNCATE is a DDL command. No triggers will be fired. Conditions like WHERE clause cannot be used with it. TRUNCATE is faster than DELETE. Note: when you issue a TRUNCATE command, it removes data directly without copying it into the Rollback Tablespace. So it is faster than DELETE. Also because of the same reason the data dele...

SQL Server String Data Types CHAR CHAR is a fixed data type. So when a column is declared as CHAR, irrespective of  the actual characters stored in that variable/column, it will use all the declared space. In the above example you can see that even though the actual length of the variable is 6, It occupies 30 bytes of space.This is because when the variable @name is declared as CHAR(30), 30 bytes of space got reserved for the variable.  Also, you can observe that CHAR type column uses 1 byte of space to store each character. Summary: 1. It is a fixed data type 2. Occupies 1 byte of space for each character 3. It is used to store non-unicode character. VARCHAR VARCHAR is a variable length data type. So when a variable or column is declared as VARCHAR, irrespective of declared space, it will use only space require to store all characters. In the above example you can see that even though the declare...