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SQL-Structured Query Language

SQL is the most common language used for creating and querying relational databases.

Many users can access a database applications with no knowledge of SQL at all.

Sites on the Web allow users to browse the catalog of the site being visited. The information about an item that is presented, such as size, color, etc. is stored in a database

The information has been retrieved using an SQL query, but the user has not issued an SQL command.

An SQL-based relational database application involves a user interface, a set of tables in the database.

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SQL-Structured Query Language

Within the RDBMS, SQL will be used to create the tables, translate user requests, maintain the data dictionary and system catalog, update and maintain the tables, establish security and carry out backup and recovery procedures.

General Syntax:

SELECT [ALL|DISTINCT] column_listFROM table_list[WHERE conditional expressions][GROUP BY group_by_column_list][HAVING conditional expressions][ORDER BY order_by_column_list]

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SQL-Structured Query Languageinserting, updating, and deleting data

Once tables have been created, it is necessery to populate them with data and maintain those data.

INSERT : is used to populate tables. exp.1) In order to enter data to each column of the tableINSERT INTO CUSTOMER VALUES(001, ‘Cavit’, ‘Tüketir’, ’13.Sok. Cuma Apt. 1/A’, ‘Bahçelievler’, ‘Ankara’);

exp.2) Data will not be entered into every column in the table;INSERT INTO CUSTOMER (CUST_ID, CUST_NAME, CUST_LNAME)VALUES (001, ‘Cavit’, ‘Tüketir’);

exp.3) Populating a table by using a subset of another table with the same structure.INSERT INTO IST_CUSTOMERSELECT * FROM CUSTOMER

WHERE CITY = ‘İST’;

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SQL-Structured Query Languageinserting, updating, and deleting data

DELETE : rows can be deleted individually or in groups. exp.1) Deleting with a certain criteriaDELETE FROM CUSTOMER

WHERE CITY = ‘İST’

exp.2) All rows;DELETE FROM CUSTOMER

UPDATE: To modify unit price in the product table to 775UPDATE PRODUCT

SET UNIT PRICE = 775WHERE PRODUCT_ID = 7;

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SQL-Structured Query Languageexpressions

Using Functions:count, min, max, sum and avg Exp 1): Select count (*)

from order_linewhere order_id = 1004;

Exp 2): Select order_id, count (*)from order_line

where order id = 1004;Count (*) counts all rows, even null! But “count” counts only the rows that contain a value.Exp 3): Select (product_name)

from product;alphabetically it shows the first product name in product table.

Using Wildcards: (*) in a Select statement selects all records according to a given condition (%) is used to represent any collection of characters. Using LIKE ‘%Desk’ when searching product name will find all different types of desks.

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SQL-Structured Query Languageexpressions

Comparison Operators:=, >, >=, <, <= ,<> or !=Exp 4: Select order_id, order_date

from orderwhere order_date > ’24-OCT-98’;

Exp 5: Select product_namefrom product

where product_name != ‘cherry’;

Using Boolean Operators:AND joins two or more conditions and returns results only when all conditions are true.OR joins two or more conditions and returns results when any condition is true.NOT negates an expression.

Ranges:The comparison operators < and > are used to establish a range of values. The keyword BETWEEN or NOT BETWEEN can also be used. .....where unit_price >199 AND unit_price <300;

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SQL-Structured Query Languageexpressions

Distinct:Sometimes when returning rows that don’t include the primary key, dublicate rows will be returned.Exp 8): Select distinct order_id, quantity

from order

IN and NOT IN Lists:To match a list of values, consider using IN.Exp 9): Select customer_name, city, state

from customerwhere state IN (‘CA’, ’TX’)

Sorting Results:The ORDER BY ClauseORDER BY sorts the final results rows in ascending or descending order.GROUP BY groups rows in an intermediate results table where the values in those rows are the same for one or more columns.HAVING can only be used following a GROUP BY and acts is a secondary WHERE clause, returning only those groups which meet a specified condition.

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SQL-Structured Query Languageusing expressions

EXAMPLES:1) SELECT PRODUCT_NAME, PRODUCT_FINISH, PRODUCT_UNIT_PRICE

FROM PRODUCTWHERE PRODUCT_NAME LIKE ‘%desk’

OR PRODUCT_NAME LIKE ‘%table’AND PRODUCT_UNIT_PRICE > 300;

2) SELECT PRODUCT_NAME, PRODUCT_UNIT_PRICEFROM PRODUCT

WHERE PRODUCT_UNIT_PRICE >199 AND PRODUCT_UNIT_PRICE<300;

3) SELECT ORDER_ID FROM ORDER_LINE;4) SELECT DISTINCT ORDER_ID FROM ORDER_LINE;5) SELECT CITY FROM CUSTOMER

GROUP BY CITYHAVING AVG(UNIT_PRICE)<760ORDER BY CITY;

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FROM identifies involved tables

WHERE Finds all rows meetingstated condition(s)

GROUP BYOrganizes rows according to values in stated column(s)

HAVING Finds all groups meeting stated condition(s)

SELECTIdentifies columns

ORDER BYSorts rows

Results

SQL-statement processing order

• Mandatory clauses are only FROM and SELECT• Processing order is different from the order of the syntax used to create statement. Each clause is processed an intermediate results table is produced that will be used for next clasuse. • Users do not see the intermediate results tables; only see the final results.