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dzina
Starting Member
Italy
4 Posts |
 Posted - 08/06/2005 : 04:29:28
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Can anybody please explain me (by simple words) which kind of joins exist and which is the different between them? I have read lots about joins but still don't have clear idea...
Thanks!! |
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madhivanan
Premature Yak Congratulator
India
22713 Posts |
Posted - 08/06/2005 : 04:53:30
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In SQL Server help file (Books On Line), type joins-SQL Server and read the topics under that
>>I have read lots about joins but still don't have clear idea...
Where are you struggling?
you should be more specific
Madhivanan
Failing to plan is Planning to fail |
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kapilarya
Yak Posting Veteran
Canada
86 Posts |
Posted - 08/06/2005 : 07:46:06
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Joins can be categorized as:
Inner joins (the typical join operation, which uses some comparison operator like = or <>). These include equi-joins and natural joins.
Inner joins use a comparison operator to match rows from two tables based on the values in common columns from each table. For example, retrieving all rows where the student identification number is the same in both the students and courses tables.
Outer joins. Outer joins can be a left, a right, or full outer join.
Outer joins are specified with one of the following sets of keywords when they are specified in the FROM clause:
LEFT JOIN or LEFT OUTER JOIN
The result set of a left outer join includes all the rows from the left table specified in the LEFT OUTER clause, not just the ones in which the joined columns match. When a row in the left table has no matching rows in the right table, the associated result set row contains null values for all select list columns coming from the right table.
RIGHT JOIN or RIGHT OUTER JOIN.
A right outer join is the reverse of a left outer join. All rows from the right table are returned. Null values are returned for the left table any time a right table row has no matching row in the left table.
FULL JOIN or FULL OUTER JOIN.
A full outer join returns all rows in both the left and right tables. Any time a row has no match in the other table, the select list columns from the other table contain null values. When there is a match between the tables, the entire result set row contains data values from the base tables.
Cross joins.
Cross joins return all rows from the left table, each row from the left table is combined with all rows from the right table. Cross joins are also called Cartesian products.
For example, here is an inner join retrieving the authors who live in the same city and state as a publisher:
USE pubs
SELECT a.au_fname, a.au_lname, p.pub_name
FROM authors AS a INNER JOIN publishers AS p
ON a.city = p.city
AND a.state = p.state
ORDER BY a.au_lname ASC, a.au_fname ASC
Kapil Arya
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Michael Valentine Jones
Yak DBA Kernel (pronounced Colonel)
USA
7020 Posts |
Posted - 08/06/2005 : 15:49:48
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You may want to start with a basic introduction to SQL programming.
Here are a couple of online courses that are a good introduction to the basics of SQL. They should be taken in sequence.
http://www.sqlcourse.com/
http://sqlcourse2.com/
The following site has a number of free training classes available: HTML, XML, SQL, .NET, Scripting, Building web sites, etc. It also offers online quizzes. The SQL Course includes a page where you can run your own queries, and a quiz.:
http://www.w3schools.com/sql/default.asp
Home Page showing all courses:
http://www.w3schools.com/default.asp
quote:
Originally posted by dzina
Can anybody please explain me (by simple words) which kind of joins exist and which is the different between them? I have read lots about joins but still don't have clear idea...
Thanks!!
CODO ERGO SUM |
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nurunseo
Starting Member
Bangladesh
6 Posts |
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JOIN
