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• Inner Join Vs Outer Join In Access
• Inner Join Vs Outer Join Performance

In this series of tips, you'll learn LEFT JOIN vs. RIGHT JOIN techniques and find examples for creating simple queries, including how to define a SQL OUTER JOIN by using multiple tables and how to use the SELECT statement and embed SQL JOINs. Joins in SQL are performed to combine the data of two different tables. An Inner Join is a condition, that results the rows, which satisfy the ‘where’ clause in “all the tables”; whereas an Outer Join is a condition that results those rows, which satisfy the ‘where’ clause in “at least one of the tables”.

To keep it simple, let me keep it this way: Considering two table A and B and internal table ITAB: Inner Join: It requires an entry with KEY of A in B, to be extracted to internal table. Outer Join: Irrespective of whether an entry exists or not in B it still extracts data from A. Eg: Table: A-Fld1Fld2-X100Y200Z300Table: B-Fld1Fld3-XabcXdefZpqr ' No entry for Key Y in table B so it is not extractedITAB fields: FLD1, FLD2, FLD3Inner Join:-FLD1FLD2FLD3-X100abcX100defZ300pqrOuter Join:-FLD1FLD2FLD3-X100abcX100defY200 ' No entry for Key Y in table B so FLD3 is blankZ300pqr. Hi,Joins are used to fetch data fast from Database tables:Tables are joined with the proper key fields to fetch the data properly.If there are no proper key fields between tables don't use Joins;Important thing is that don't USE JOINS FOR CLUSTER tableslike BSEG and KONV.Only use for Transparenmt tables.You can also use joins for the database VIews to fetch the data.JOINS.

Inner Join Vs Outer Join In Access

FROM tabref1 INNER JOIN tabref2 ON condEffectThe data is to be selected from transparent database tables and/or views determined by tabref1 and tabref2. Tabref1 and tabref2 each have the same form as in variant 1 or are themselves Join expressions. The keyword INNER does not have to be specified. The database tables or views determined by tabref1 and tabref2 must be recognized by the ABAP Dictionary.In a relational data structure, it is quite normal for data that belongs together to be split up across several tables to help the process of standardization (see relational databases).

Inner Join Vs Outer Join Performance

To regroup this information into a database query, you can link tables using the join command. This formulates conditions for the columns in the tables involved.

An inner join returns rows that can be combined based on the join criteria.An outer join returns these and all rows.from the first table for a left join.from the second table for a right join.from both tables for a full joinChoosing when to use one or the other is a matter of determining what data you need. For your example if you need only records that have userids from telephone that match ids in user then use the inner join. If you also want to include rows from user that have no matching telephone entry, then the left join would be appropriate.For more information see. Outer join is expressly designed to produce nulls in its result and should therefore be avoided, in general. Relationally speaking, it's a kind of shotgun marriage: It forces tables into a kind of union—yes, I do mean union, not join—even when the tables in question fail to conform to the usual requirements for union. It does this, in effect, by padding one or both of the tables with nulls before doing the union, thereby making them conform to those usual requirements after all.

But there's no reason why that padding shouldn't be done with proper values instead of nulls, as in this example: SELECT SNO, PNOFROM SPUNIONSELECT SNO, 'nil' AS PNOFROM SWHERE SNO NOT IN ( SELECT SNO FROM SP )Alternatively, the same result could be obtained by using the SQL outer join operator in conjunction with COALESCE, as here: SELECT SNO, COALESCE ( PNO, 'nil' ) AS PNOFROM ( S NATURAL LEFT OUTER JOIN SP ) AS TEMP. An inner join is a join where the only results displayed are results where the keys are in both tables. An outer join will display the results for all keys in one tables, a left join from the first and a right join from the second. Since you have asked when to use what, here is a scenario with queries - select which to use depending on the requirement.Data:Table Users has 10 records.Table Phoneno has 6 records (with a 1:1 relation, meaning that an entry in PhoneNo will reference only one entry in Users, and only one entry in PhoneNo can reference a given entry in Users).Requirement 1: Show all users with their phone numbers. Ignore users without phone number.Query: SELECT u.uid, u.name, p.phonnoFROM user uINNER JOIN phones p ON p.uid = u.uidResult: shows 6 users who has phone numberRequirement 2: Show all users with their phone number. If user does not have a phone display 'N/A' (not available)Query: SELECT u.uid, u.name, ifnull(p.phonno,'N/A')FROM user uLEFT OUTER JOIN phones p ON p.uid = u.uidResult:Shows all 10 recordsNote: ifnull is a MySql syntax to transform the null value.

I used this function to make the db engine show 'N/A' when phonno is null. Look for appropriate function if you are using some other DBMS. In SQL Server you have to use the CASE statement.I hope this helps.