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Querying and Reporting Module 3

Arithmetic operators used in SQL Built in Functions Retrieving data with the select statements Grouping Results sets Joins Sub queries Learning Objectives

At the end of this section, you should be able to work with: Arithmetic operators used in SQL Built in Functions String Functions Date Functions System Functions Aggregate Functions Retrieving data with the select statements Based on Conditions Limit Results Module 3 : Agenda

Module 3 : Agenda Grouping Results sets Group by Compute and Compute By Joins Natural Join Equi Join Self Join Outer Join Sub queries In Exists Correlated sub queries

SELECT Statement Use the SELECT statement to retrieve data from one or more tables: SELECT <column(s) > FROM <table> [ WHERE <condition>] [ ORDER BY <column(s) [ASC|DESC]>] table is the name of the table column is the name of the column in the table to be selected condition identifies the rows to be selected and is composed of column names, expressions, constraints, sub-queries and comparison operators column is the name of the column(s) used for sorting (order by)

Querying and Reporting Selection : Querying for selection retrieves a subset of the rows in one or more tables. Example Projection : Querying for projection retrieves a subset of the columns in one or more tables. It is best to put each column chosen in a separate line Example SELECT * FROM emp SELECT empno, ename, deptno FROM emp

Rearranging order of columns: Example Using Column aliases Example Querying and Reporting (Continued) SELECT ename as [Employee Name], empno, deptno FROM emp SELECT empname, eno, deptno FROM emp

Arithmetic Operators Modulo % Division / Addition + Multiplication * Subtraction - Operation Operator

Built in Functions Built in Functions are a T-SQL extension to SQL String Functions Date Functions System Functions Aggregate Functions

Built In Functions : String Functions Returns part of a string. Start s pecifies the character position at which the substring begins. length specifies the number of characters in the substring. substring ( expression , start , length ) Returns the reverse of the character or binary expression reverse ( expression ) Returns an integer representing the number of characters in a character expression or text value. char_length ( char_expr ) Returns the ASCII code for the first character in the expression. ascii ( char_expr ) Descriptions Functions

Built In Functions : Date Functions Returns date produced by adding datepart to given date. dateadd ( datepart , number, date ) Returns the time between the first and second date. You can specify the datepart as months, years, hours, etc. datediff (datepart, date, date) Returns part of date as an integer. datepart ( datepart, date ) Returns Current system date and time. getdate () Descriptions Functions

Built In Functions : System Functions Returns the length of the column datalength ( expression ) Returns the computer name Host_name () Returns the process id of the process. host_id ( ) Descriptions Functions

Use of Aggregate Functions Aggregate functions are used to summarize the data retrieved in a query. Total of the (distinct) values in the expression Sum ([all | distinct] expression ) Lowest value in the expression Min ( expression ) Highest value in the expression Max ( expression ) Number of selected rows – including null values count(*) Number of (distinct) non-null values in the expression Count ([all | distinct] expression ) Average of the (distinct) values in the expression Avg ([all | distinct] expression ) Description Aggregate Function

Selecting Rows – Search Based The method of restriction is the basis of the WHERE clause in SQL Character strings and dates in the WHERE clause must be enclosed in single quotation marks (‘)

Rows may be limited by: EQUALS CONDITION Display rows based on an exact match of values SELECT LastName, Salary FROM Employee WHERE Salary = 30000 SELECT EmployeeId, LastName FROM Employee WHERE ManagerName = ‘RAYMOND’

Rows may be limited by: (Continued) >, <, <=, >= or <> CONDITION SELECT LastName FROM Employee WHERE Salary > 30000 SELECT EmployeeId, LastName FROM Employee WHERE Salary <= 30000 SELECT EmployeeId FROM Employee WHERE Status <> ‘ACTIVE’

Rows may be limited by: (Continued) BETWEEN CONDITION Display rows based on a range of values SELECT LastName FROM Employee WHERE Salary BETWEEN 30000 AND 50000 IN CONDITION Display rows based on a list of values SELECT EmployeeId FROM Employee WHERE ManagerId IN (100, 200, 300)

Rows may be limited by: (Continued) LIKE CONDITION Performs wildcard searches of valid search string values Can contain either literal characters or numbers % denotes zero or many characters _ denotes one character Use ESCAPE identifier to search for the actual % and _symbols SELECT LastName FROM Employee WHERE LastName LIKE ‘%ram’ SELECT LastName FROM Employee WHERE LastName LIKE ‘_at’

Rows may be limited by: (Continued) LOGICAL CONDITION AND, OR, NOT SELECT LastName , JobId FROM Employee WHERE Salary <= 15000 AND JobId = ‘SE’ SELECT LastName , JobId FROM Employee WHERE Salary <= 15000 OR JobId = ‘SE’

Rows may be limited by: (Continued) LOGICAL CONDITION AND, OR, NOT SELECT LastName , JobId FROM Employee WHERE Salary <= 15000 AND NOT JobId = ‘SE’

Rows may be limited by: (Continued) Distinct Top Percent SELECT distinct au_id , FROM titleauthor SELECT Top(4) * FROM titleauthor SELECT Top 20 percent * FROM titleauthor

Sorting Rows ORDER BY clause ASC specifies an ascending order DESC specifies a descending order SELECT LastName, Salary , JobId FROM Employee ORDER BY Salary DESC, JobId ASC Display the result in descending order by the attribute salary If two records have the same attribute value, the salary sorting criteria is in ascending order according to the attribute values of JobId

Group By – A group by expression can contain column names not present in the select list. Grouping Result Sets SELECT type, avg(price), sum(ytd_sales) FROM title s Group by pub_id, type

Compute clause provides a detail and summary rows with one select statement. You can calculate more than one row aggregate. Grouping Result Sets SELECT type, price, advance FROM title s Order by type Compute sum(price), sum(advance) SELECT type, price, advance FROM title s Order by type Compute sum(price), sum(advance) By type

Joins Joins compare two or more tables or views by specifying compare column. It checks values in these columns row wise and links the rows with the matching values. Joins can be applied to the tables of the own database or other databases (with select permissions)

start of select, update, insert, delete, or subquery from { table_list | view_list } where [not] [ table_name . | view_name .] column_name join_operator [ table_name . | view_name .] column_name [{and | or} [not] [ table_name .| view_name .] column_name join_operator [ table_nam e.| view_name .] column_name ]... End of select, update, insert, delete, or subquery Joins - Syntax

Joins – Cross Join When a join is applied without the WHERE clause it produces the Cartesian product of the tables involved in that join. USE AdventureWorks GO SELECT p.SalesPersonID, t.Name AS Territory FROM Sales.SalesPerson p CROSS JOIN Sales.SalesTerritory t ORDER BY p.SalesPersonID;

Joins – Equi Join and Natural Join Joins based on equality are called as Equi Joins When an Equi-join returns all the columns of both the tables it is known as Natural Join SELECT au_fname, pub_name FROM Authors, Publishers Where Authors.city=Publishers.city SELECT * FROM Authors, Publishers Where Authors.city=Publishers.city

Joins – Self Join When a join compares values within the same column of one table are called as self joins. USE pubs; GO select au1.au_fname, au2.au_fname, from authors au1, authors au2 where au1.city = "Oakland" and au2.city = "Oakland" and au1.state = "CA" and au2.state = "CA" and au1.postalcode = au2.postalcode

Joins – Outer Join Outer joins include all the rows regardless of whether there are matching rows. Outer Joins are of 3 types Left Outer Right Outer Full Outer SELECT * FROM titles LEFT JOIN titileauthor ON titiles.title_id = titleauthor.title_id

Joins – Outer Join SELECT * FROM titles RIGHT JOIN titileauthor ON titiles.title_id = titleauthor.title_id SELECT * FROM titles FULL OUTER JOIN titileauthor ON titiles.title_id = titleauthor.title_id

Sub Queries A subquery is nested select statement in another select/insert/update/delete statement as a condition. A subquery can be used as an expression. When subquery can be evaluated as if it were an independent query it is called a Non correlated subquery. When a subquery can not be evaluated as an independent query, but can reference columns in a table listed in the from list of the outer query, it is called a correlated subquery. There are two types of subqueries Expression subqueries Quantified predicate subqueries

Sub Queries (Continued) Expression subqueries: The value retuned is always single value which is further used for comparison. SELECT title, price FROM titles WHERE price = ( SELECT price FROM titles WHERE title = 'Straight Talk About Computers')

Sub Queries (Continued) Quantified predicate subqueries: The value returned can range from 0..n. This query operates on lists introduced with IN or with a comparison operator. Further it can be used as an existence test with the EXISTS introduced with exists. Subqueries with IN SELECT pub_name FROM publishers WHERE pub_id IN (SELECT pub_id FROM titles WHERE type = ‘business’)

Subqueries with Exists Sub Queries (Continued) SELECT pub_name FROM publishers WHERE EXISTS (SELECT * FROM titles WHERE pub_id = publishers.pub_id AND type = ‘business’)

Correlated Subqueries Sub Queries (Continued) SELECT table1.type FROM titles table1 WHERE table1.type IN (SELECT table2.type FROM titles table2 WHERE table1. pub_id ! = table2. pub_id )

You may find useful content on T-SQL joins on the following url: Web sites: http://www.sqlteam.com/article/writing-outer-joins-in-t-sql http://www.sqlmag.com/Article/ArticleID/5342/sql_server_5342.html http://pietschsoft.com/post/2005/12/T-SQL-Join-Tables-by-a-Field-that-contains-a-delimited-string.aspx ms-help://MS.SQLCC.v9/MS.SQLSVR.v9.en/udb9/html/c4f98374-e8a7-4f73-8d0e-309bd94ad1ae.htm Resources

Key Points SQL is an industry standard language for updating to, and getting information from, a database. The basic and most common SQL statements are: SELECT, INSERT, UPDATE, DELETE.

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