sql basics for software development part 1

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Basics of SQL

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SQLDatabaseTableStatementsOperatorsData typesConstraintsKeysIndexesFunctions

Index

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What is SQL? Standard language for accessing databases SQL stands for Structured Query Language Lets you access and manipulate databases Nonprocedural language It is an ANSI (American National Standards Institute) standard

Introduction

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A database is an organized collection of data, typically stored in electronic format: It allows you to input, manage, organize, and retrieve data quickly Traditional databases are organized by records (rows), fields (columns) stored in tables which

are stored in the database files It supports storage and manipulation of data It makes easy data management

Database




A database table is a collection of rows and columns that is used to organize information about a single topic

Each row within a table corresponds to a single record and contains several attributes that describe the row

These tables are stored in databases

Table in SQL




SQL Statements Data Definition Language(DDL)

• This statements are used to alter/modify a database or table structure and schema. These statements handle the design and storage of database objects• It include the following:

• CREATE – create a new Table, database, schema• ALTER – alter existing table, column description• DROP – delete existing objects from database




SQL Statements

DML (Data Manipulation Language)These statements affect records in a table. These are basic operations we perform on data such

as selecting a few records from a table, inserting new records, deleting unnecessary records, and updating/modifying existing records

It include the following:SELECT – select records from a table INSERT – insert new recordsUPDATE – update/Modify existing recordsDELETE – delete existing records




SQL Statements

Data Control Language(DCL)These statements control the level of access that users have on database objects It includes the following:

GRANT – allows users to read/write on certain database objects REVOKE – keeps users from read/write permission on database objects

Transaction Control Language(TCL)These statements allow you to control and manage transactions to maintain the integrity of data within SQL

statements BEGIN Transaction – opens a transaction COMMIT Transaction – commits a transaction ROLLBACK Transaction – ROLLBACKs a transaction in case of any error




SQL (Cont.) SQL Data Definition Commands:

COMMAND OR OPTION DESCRIPTION

CREATE SCHEMA AUTHORIZATION CREATE TABLE NOT NULL UNIQUE PRIMARY KEY FOREIGN KEY DEFAULT CHECK CREATE INDEX CREATE VIEW ALTER TABLE CREATE TABLE AS DROP TABLE DROP INDEX DROP VIEW

Creates a database schemaCreates a new table in the user’s database schemaEnsures that a column will not have null valuesEnsures that a column will not have duplicate valuesDefines a primary key for a tableDefines a foreign key for a tableDefines a default value for a column (when no value is given)Constraint used to validate data in an attributeCreates an index for a tableCreates a dynamic subset of rows/columns from one or more tablesModifies a table's definition (adds, modifies, or deletes attributes or constraints)Creates a new table based on a query in the user's database schemaPermanently deletes a table (and thus its data)Permanently deletes an indexPermanently deletes a view




SQL (Cont.) SQL Data Manipulation Commands:

COMMAND OR OPERATION DESCRIPTION

INSERT Inserts row(s) into a table

SELECTWHEREGROUP BYHAVINGORDER BY

Selects attributes from rows in one or more tables or viewsRestricts the selection of rows based on a conditional expressionGroups the selected rows based on one or more attributesRestricts the selection of grouped rows based on a conditionOrders the selected rows based on one or more table’s rows

UPDATE Modifies an attribute’s values in one or more table’s rows

DELETE Deleted one or more rows from a table

COMMIT Permanently saves data changes

ROLLBACK Restores data to their original values




SQL Operators

COMPARISON OPERATION =,<,>,<=,>=,<> Used in conditional expressions

LOGICAL OPERATION AND/OR/NOT Used in conditional expressions

ARITHMETIC OPERATION +,-,*,/,%

Used in conditional expressions

SPECIAL OPERATION BETWEEN IS NULL LIKE IN EXISTS DISTINCT

Used in conditional expressionsChecks whether an attribute value is within a rangeChecks whether an attribute value is nullChecks whether an attribute value matches a given string patternChecks whether an attribute value matches any value within a value listChecks whether a subquery returns any rowsLimits values to unique values

Aggregate Functions COUNT MIN MAX SUM AVG

Used with SELECT to return mathematical summaries on columnsReturns the number of rows with non-null values for a given columnReturns the minimum attribute value found in a given columnReturns the maximum attribute value found in a given columnReturns the sum of all values for a given columnReturns the average of all values for a given column




Data Types It defines what kind of value a column can contain Selection is usually dictated by nature of data and by intended use Pay close attention to expected use of attributes for sorting and data retrieval purposes




Data Types (Cont.)

Character CHAR(L)

VARCHAR(L) orVARCHAR2(L)

Fixed-length character data for up to 255 characters. If you store strings that are not as long as the CHAR parameter value, the remaining spaces are left unused. Therefore, if you specify CHAR(25), strings such as "Smith" and "Katzenjammer" are each stored as 25 characters. However, a U.S. area code is always three digits long, so CHAR(3) would be appropriate if you wanted to store such codes.

Variable-length character data. The designation VARCHAR2(25) will let you store characters up to 25 characters long. However, VARCHAR will not leave unused spaces. Oracle users may use VARCHAR2 as well as VARCHAR.

Date DATE Stores dates in the Julian date format




SQL Constraints

NOT NULL - Indicates that a column cannot store NULL value CHECK - Ensures that the value in a column meets a specific condition DEFAULT - Specifies a default value when specified none for this column




SQL Keys

Unique - Ensures that each row for a column must have a unique value Primary Key - A combination of a NOT NULL and UNIQUE. Ensures that a column (or combination of two or more columns) have an unique identity which helps to find a particular record in a table more easily and quickly, each table can have only ONE primary key Foreign Key - Ensure the referential integrity of the data in one table to match values in another table, A FOREIGN KEY in one table points to a PRIMARY KEY in another table Composite Key - Combination of two or more columns in a table that can be used to uniquely identify each row in the table when the columns are combined uniqueness is guaranteed, but when it taken individually it does not guarantee uniqueness Candidate Key- It is candidate for primary key of a table, In simple words we can understand that such type of keys which full fill all the requirements of primary key which is not null and have unique records is a candidate for primary key




SQL Indexes

Clustered• Clustered indexes sort and store the data rows in the table or view based on their key values. These are

the columns included in the index definition • There can be only one clustered index per table, because the data rows themselves can be sorted in only

one order

Non clustered• Non clustered indexes have a structure separate from the data rows• A non clustered index contains the non clustered index key values and each key value entry has a pointer

to the data row that contains the key value




SQL Functions

SQL has many built-in functions for performing calculations on data• SQL Aggregate functions• SQL Scalar Functions




SQL Aggregate Functions

It returns a single value, calculated from values in a column Useful aggregate functions:

• AVG() - Returns the average value• COUNT() - Returns the number of rows• FIRST() - Returns the first value• LAST() - Returns the last value• MAX() - Returns the largest value• MIN() - Returns the smallest value• SUM() - Returns the sum

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SQL Scalar functions

It returns a single value, based on the input value Useful scalar functions:

• UCASE() - Converts a field to upper case• LCASE() - Converts a field to lower case• MID() - Extract characters from a text field• LEN() - Returns the length of a text field• ROUND() - Rounds a numeric field to the number of decimals specified• NOW() - Returns the current system date and time• FORMAT() - Formats how a field is to be displayed




http://www.w3schools.com/sql/ http://www.tutorialspoint.com/sql/

References




sql basics for software development part 1

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