DATETIME SELECT SELECT INTO DATE PAD STRING DYNAMIC SQL CURSOR MONEY FORMAT PERCENT STORED PROCEDURE SQL SERVER AGENT JOB OPTIMIZATION WHILE LOOP OVER PARTITION BY UPDATE
SITE SEARCH SQLUSA.com HEADLINES NEWS
SQL E/BOOKS   SQL 2014 PROGRAMMING   DOWNLOADS
SCRIPTS SQL 2005 SQL 2008 ARTICLES
SQL JOBS TWITTER FORMAT VIDEOS
How to use LEFT JOIN in queries?

Execute the following T-SQL example scripts in SQL Server Management Studio Query Editor to demonstrate the application of the LEFT JOIN between two tables.

-- Simple left join - all left table rows included - QUICK SYNTAX

-- Missing right table rows have null values (translated to -1 by isnull)

USE AdventureWorks2008;

GO

SELECT p.Name                       AS ProductName,

      ISNULL(pr.ProductReviewID,-1) AS ReviewID

FROM Production.Product p

  LEFT JOIN Production.ProductReview pr

    ON p.ProductID = pr.ProductID

ORDER BY ProductName

/* ProductName          ReviewID

....

HL Mountain Handlebars  -1

HL Mountain Pedal       2

HL Mountain Pedal       3

HL Mountain Rear Wheel  -1  ....*/

------------

 

------------

-- LEFT JOIN predicate vs. WHERE clause predicate

-- They are not the same (they are the same for inner join)

------------

SELECT RowsCount=COUNT(*)

FROM Production.Product p

  LEFT JOIN Production.ProductReview pr

    ON p.ProductID = pr.ProductID

    AND Color = 'Red'

-- 504

 

SELECT RowsCount=COUNT(*)

FROM Production.Product p

  LEFT JOIN Production.ProductReview pr

    ON p.ProductID = pr.ProductID

WHERE Color = 'Red'

-- 38

------------

 

Related articles:

SQL SERVER Better Performance LEFT JOIN or NOT IN?

http://www.sqlusa.com/bestpractices2005/advancedsql/employeegeoreport/

 

Exam Prep 70-461
Exam 70-461
DATETIME SELECT SELECT INTO DATE PAD STRING DYNAMIC SQL CURSOR MONEY FORMAT PERCENT STORED PROCEDURE SQL SERVER AGENT JOB OPTIMIZATION WHILE LOOP OVER PARTITION BY UPDATE