sql sql server : overview sql : overview types of sql database : creation tables : creation &...
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SQL SQL Server : Overview SQL : Overview Types of SQL Database : Creation Tables : Creation & Manipulation Data : Creation & Manipulation Data : Retrieving using SQL
SQL : Overview Is the standard command set used to
communicate with the relational database management systems
Can do Creating databases, Creating tables, Querying and Manipulating data and granting access to the users
English like structure is by nature flexible
Types of SQL Commands SQL statements are divided into the following
categories Data Definition Language (DDL) Data Manipulation Language (DML) Data Query Language (DQL) Data Control Language (DCL) Data Administration Statements (DAS) Transaction Control Statements (TCS)
Data Definition Language Is used to create, alter and delete database
objects The commands used are
CREATE ALTER DROP
Data Manipulation Language Used to insert data into the database,
modify and delete the data in the database Three DML statements
INSERT UPDATE DELETE
Data Query Language This statement enables you to query one or
more tables to get the information commonly used SQL statements SQL has only one data query statement
SELECT
Data Control Language The DCL consists of commands that
control the user’s access to the database objects
The DCL is mainly related to the security issues
The DCL commands are GRANT - Giving access to the data REVOKE - Denying access to the data
Data Administration Statements DASs allow the user to perform audits and
analysis on operations within the database. Used to analyze the performance of the
system Data Administration commands are
START AUDIT STOP AUDIT
Transaction Control Statements TCSs are statements, which manage all the
changes made by the DML statements Some of the TCSs are
COMMIT ROLLBACK SAVEPOINT SET TRANSACTION
Databases Collection of related data and manipulation
of that data Can create database using SQL command
CREATE DATABASE databasename
Tables Are the basic building blocks in any
RDBMS contains rows and columns of data using DDL commands, we can create ,
alter and delete tables Creation of table includes the properties of
the columns
Create statementCREATE TABLE table-name
(column-1-definition
[,column-2-definition] …..
[,column-n-definition]
[,primary key (column name)]
[.alternate key (column name)]
[,Foreign key (column name) ]);
Column definition columnName data-type [NULL | NOT NULL
[WITH DEFAULT | UNIQUE]]
NULL - RDBMS insert a null in that column if the user does not specify a value
NOT NULL - column should have a value WITH DEFAULT - the RDBMS will substitute
the default values UNIQUE - no duplicate values will be allowed
Data types char(n) - represents a fixed length of string of ‘n’
characters where n>0 and is an integer varchar(n) - varying length string whose max
length is ‘n’ bit(n) - represents a fixed length string of exactly
‘n’ bits decimal(p, q) - represents a decimal number, ‘p’
digits and with decimal point ‘q’ digits from right
Data Types float(n) - represents the floating point
number int - represents a signed integer datetime - represents the date/time money - represents the currency
2nd form of CREATE CREATE TABLE new-table-name LIKE
table-name when a table is created from an existing
table only the structure is copied; the primary, alternate and foreign key definitions is not inherited
Modifying a Table An existing table can be modified by using
the ALTER TABLE statement ALTER TABLE table-name
ADD column definition ALTER TABLE table-name
Add CONSTRAINT constraint name
Primary key (column name)
Deleting a table An existing table can be deleted at any
time by using the DROP TABLE statement DROP TABLE table-name specified table is deleted from the system all the data for that table also will be
deleted
Inserting rows into a table INSERT INTO table-name
[[column [,column]….]]
values [literal[,literal]…]]; a single row is inserted into the table, having
specified columns INSERT INTO table-name
[[column [,column]….]]
subquery; the subquery is evaluated first and a copy of the
result(usually multiple rows) is inserted into the table
Updating fields in a row UPDATE table-name
SET column-name = expr
[WHERE condition] table-name : table for the data to be updated SET clause : the set of new values to be set WHERE clause : condition will be checked
and particular record gets updated
Deleting of data from the table DELETE FROM table-name
WHERE condition Depending on the condition the record will
be deleted from the table
SELECT statements SELECT - A keyword that tells the
database this command is a query. All queries begin with this word followed by a space
the select command simply instructs the database to retrieve information from a table
Different features applied to a simple statement All columns Qualified Retrieval Eliminating Duplicates Using Boolean(IN, BETWEEN, LIKE) Using Escape clause Computed values Involving nulls
All Columns SELECT * FROM Table-name
Qualified Retrieval SELECT * FROM table-name
WHERE condition can use all comparision operators (=, <>, <, >, <=,
>=) in the WHERE clause can contain multiple comparison with AND, OR,
NOT Eliminating Duplicates
SELECT DISTINCT column-name FROM table-name
Using Boolean Operators IN
SELECT * FROM table-name
WHERE column-name IN (val1, val2, val3…); BETWEEN
SELECT * FROM table-name
WHERE column-name BETWEEN val1 and val2 between is an inclusive operator values matching either of the boundary values
cause the predicate to be true
NOT BETWEEN SELECT * FROM table-name
WHERE column-name NOT BETWEEN val1 and val2
LIKE SELECT * FROM table-name
WHERE column-name LIKE ‘string%’ LIKE ‘_%’
Escape Sequence SELECT * FROM table-name
WHERE column-name LIKE ‘%\_%’