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Posts Tagged ‘Database’

Understanding sys.objects:

Sys.objects is a system VIEW in SQL Server 2005, for each SQL database there is a separate sys.object view which gets stored within databse itself.

Using Sys.objects returns list of all database objects and its types, type can be either of given below:

DB OBJECT TYPES

F     FOREIGN_KEY_CONSTRAINT

IT    INTERNAL_TABLE

PK    PRIMARY_KEY_CONSTRAINT

S     SYSTEM_TABLE

SQ    SERVICE_QUEUE

U     USER_TABLE

V     VIEW

How to DELETE all User Tables , stored procedures , UDF’s and Views using cursor

Use [database name]

declare @q nvarchar(max)

declare @name nvarchar(max);

declare @type nvarchar(max);

declare cur cursor for

select name ,type from sys.objects where type in(‘p’,‘fn’,‘v’,‘u’);

open cur;

fetch next from cur into @name,@type

while @@fetch_status = 0

begin

if(@type=‘p’)

begin

set @q=N‘drop procedure ‘ + @name;

end

if(@type=‘fn’)

begin

set @q=N‘drop function ‘ + @name;

end

if(@type=‘v’)

begin

set @q=N‘drop view ‘ + @name;

end

if(@type=‘u’)

begin

set @q=N‘drop table ‘ + @name;

end

exec sp_executesql @q;

fetch next from cur into @name,@type

end

close cur;

deallocate cur;

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Normalization: is a process of organizing data and minimizing redundancy

De-normalization: is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

Stored Procedure: is a named group of T-SQL statements which can be created and stored in Database as an object.

Primary Key: is a unique identifier of a row in a DB table, [it can’t be NULL]

Unique key: forces uniqueness to a respective table column, [it can be NULL]

Foreign Key: a foreign key in 1 table refers to the primary key in other table, Used to force referential integrity.

Inner join: exists in both tables

Left Outer join: all records from left side table + matched rows from right side table (totals number of rows will be same as left table)

Right Outer join: all records from right side table + matched rows from left side table (totals number of rows will be same as right table), it’s a mirror image of left outer join

Full Outer join: all records from left side table + all records from right side table, weather matched or not

Cross join: returns [left table rows * right table rows], a Cartesian product of both tables

Self join: when table joins to itself using diff aliases to avoid confusion

Union: selects only distinct records from both tables

Union all: selects all records from both tables

View: is a subset of a table, can be used to retrieve data, insert or Update data. Can contain multiple select statements inside

Trigger: A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs.

Cursor: is a database object used to loop trough records on row by row bases.

Index: pointers to data records, represents structure of how data get stored physically in a table

Clustered index Non clustered index
Reorders physical data stored in table It contains pointers to data rows
A table can have Only 1 clustered index A table can have one OR many non-clustered index
Table is having By default a clustered index
Leaf nodes contains data Leaf nodes contains reference to data

Linked server: is a concept of adding other remote server to a group to query DB’s of both servers together

Collation: set of rules that determines how data stores & compares in database

Collation types: case sensitive, accent sensitive, kana sensitive, width sensitive

Data ware housing:

  1. Record should Never delete from DB
  2. All records must be linked
  3. Once committed records should be read-only
  4. All changes made must be tracked with time

User defined function (UDF): is a bunch of T-SQL statements which accepts 0 or more parameters and returns a scalar data value or table.

DDL: data definition language – e.g. TRUNCATE command is a DDL command

DML: data manipulation language – e.g. INSERT, UPDATE & DELETE are DML commands

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