topic Re: Joins in Application Development and Automation Discussions

Joins

Former Member — Wed, 15 Feb 2006 17:06:49 GMT

Hi all,

Can anyone exlain me what is the difference between inner join and outer join ? Also please provide me with a sample syntax for both the joins. Are joins applicable to views alone ?

Regards,

Varun.

Re: Joins

former_member181966 — Wed, 15 Feb 2006 17:09:45 GMT

Check out the post :

Plz also award point .

Thanks

Re: Joins

Former Member — Wed, 15 Feb 2006 17:10:35 GMT

Hi Varun,

IF you press F1 on JOIN statement ,it has explained really good.I am pasting the same for you.

... FROM tabref1 [INNER] JOIN tabref2 ON cond

Effect

The 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). 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. The inner join contains all combinations of lines from the database table determined by tabref1 with lines from the table determined by tabref2, whose values together meet the logical condition (join condition) specified using ON>cond.

Inner join between table 1 and table 2, where column D in both tables in the join condition is set the same:

Table 1 Table 2

|--|||--|

\ /

Inner Join

|--||||||||--|

| A | B | C | D | D | E | F | G | H |

|--||||||||--|

| a1 | b1 | c1 | 1 | 1 | e1 | f1 | g1 | h1 |

| a2 | b2 | c2 | 1 | 1 | e1 | f1 | g1 | h1 |

| a4 | b4 | c4 | 3 | 3 | e2 | f2 | g2 | h2 |

|--||||||||--|

Example

Output a list of all flights from Frankfurt to New York between September 10th and 20th, 2001 that are not sold out:

DATA: DATE LIKE SFLIGHT-FLDATE,

CARRID LIKE SFLIGHT-CARRID,

CONNID LIKE SFLIGHT-CONNID.

SELECT F_{CARRID F}CONNID F~FLDATE

INTO (CARRID, CONNID, DATE)

FROM SFLIGHT AS F INNER JOIN SPFLI AS P

ON F_{CARRID = P}CARRID AND

F_{CONNID = P}CONNID

WHERE P~CITYFROM = 'FRANKFURT'

AND P~CITYTO = 'NEW YORK'

AND F~FLDATE BETWEEN '20010910' AND '20010920'

AND F_{SEATSOCC < F}SEATSMAX.

WRITE: / DATE, CARRID, CONNID.

ENDSELECT.

If there are columns with the same name in both tables, you must distinguish between them by prefixing the field descriptor with the table name or a table alias.

Note

In order to determine the result of a SELECT command where the FROM clause contains a join, the database system first creates a temporary table containing the lines that meet the ON condition. The WHERE condition is then applied to the temporary table. It does not matter in an inner join whether the condition is in the ON or WHEREclause. The following example returns the same solution as the previous one.

Example

Output of a list of all flights from Frankfurt to New York between September 10th and 20th, 2001 that are not sold out:

DATA: DATE LIKE SFLIGHT-FLDATE,

CARRID LIKE SFLIGHT-CARRID,

CONNID LIKE SFLIGHT-CONNID.

SELECT F_{CARRID F}CONNID F~FLDATE

INTO (CARRID, CONNID, DATE)

FROM SFLIGHT AS F INNER JOIN SPFLI AS P

ON F_{CARRID = P}CARRID

WHERE F_{CONNID = P}CONNID

AND P~CITYFROM = 'FRANKFURT'

AND P~CITYTO = 'NEW YORK'

AND F~FLDATE BETWEEN '20010910' AND '20010920'

AND F_{SEATSOCC < F}SEATSMAX.

WRITE: / DATE, CARRID, CONNID.

ENDSELECT.

Note

Since not all of the database systems supported by SAP use the standard syntax for ON conditions, the syntax has been restricted. It only allows those joins that produce the same results on all of the supported database systems:

Only a table or view may appear to the right of the JOIN operator, not another join expression.

Only AND is possible in the ON condition as a logical operator.

Each comparison in the ON condition must contain a field from the right-hand table.

If an outer join occurs in the FROM clause, all the ON conditions must contain at least one "real" JOIN condition (a condition that contains a field from tabref1 amd a field from tabref2.

Note

In some cases, '*' may be specified in the SELECT clause, and an internal table or work area is entered into the INTO clause (instead of a list of fields). If so, the fields are written to the target area from left to right in the order in which the tables appear in the FROM clause, according to the structure of each table work area. There can then be gaps between table work areas if you use an Alignment Request. For this reason, you should define the target work area with reference to the types of the database tables, not simply by counting the total number of fields. For an example, see below:

Variant 3

... FROM tabref1 LEFT [OUTER] JOIN tabref2 ON cond

Effect

Selects the data from the transparent database tables and/or views specified in tabref1 and tabref2. tabref1 und tabref2 both have either the same form as in variant 1 or are themselves join expressions. The keyword OUTER can be omitted. The database tables or views specified in tabref1 and tabref2 must be recognized by the ABAP-Dictionary.

In order to determine the result of a SELECT command where the FROM clause contains a left outer join, the database system creates a temporary table containing the lines that meet the ON condition. The remaining fields from the left-hand table (tabref1) are then added to this table, and their corresponding fields from the right-hand table are filled with ZERO values. The system then applies the WHERE condition to the table.

Left outer join between table 1 and table 2 where column D in both tables set the join condition:

Table 1 Table 2

|--|||--|

\ /

Left Outer Join

|--||||||||--|

| A | B | C | D | D | E | F | G | H |

|--||||||||--|

| a1 | b1 | c1 | 1 | 1 | e1 | f1 | g1 | h1 |

| a2 | b2 | c2 | 1 | 1 | e1 | f1 | g1 | h1 |

| a3 | b3 | c3 | 2 |NULL|NULL|NULL|NULL|NULL|

| a4 | b4 | c4 | 3 | 3 | e2 | f2 | g2 | h2 |

|--||||||||--|

Example

Output a list of all custimers with their bookings for October 15th, 2001:

DATA: CUSTOMER TYPE SCUSTOM,

BOOKING TYPE SBOOK.

SELECT SCUSTOM_{NAME SCUSTOM}POSTCODE SCUSTOM~CITY

SBOOK_{FLDATE SBOOK}CARRID SBOOK_{CONNID SBOOK}BOOKID

INTO (CUSTOMER-NAME, CUSTOMER-POSTCODE, CUSTOMER-CITY,

BOOKING-FLDATE, BOOKING-CARRID, BOOKING-CONNID,

BOOKING-BOOKID)

FROM SCUSTOM LEFT OUTER JOIN SBOOK

ON SCUSTOM_{ID = SBOOK}CUSTOMID AND

SBOOK~FLDATE = '20011015'

ORDER BY SCUSTOM_{NAME SBOOK}FLDATE.

WRITE: / CUSTOMER-NAME, CUSTOMER-POSTCODE, CUSTOMER-CITY,

BOOKING-FLDATE, BOOKING-CARRID, BOOKING-CONNID,

BOOKING-BOOKID.

ENDSELECT.

If there are columns with the same name in both tables, you must distinguish between them by prefixing the field descriptor with the table name or using an alias.

Note

For the resulting set of a SELECT command with a left outer join in the FROM clause, it is generally of crucial importance whether a logical condition is in the ON or WHERE condition. Since not all of the database systems supported by SAP themselves support the standard syntax and semantics of the left outer join, the syntax has been restricted to those cases that return the same solution in all database systems:

Only a table or view may come after the JOIN operator, not another join statement.

The only logical operator allowed in the ON condition is AND.

Each comparison in the ON condition must contain a field from the right-hand table.

Comparisons in the WHERE condition must not contain a field from the right-hand table.

The ON condition must contain at least one "real" JOIN condition (a condition in which a field from tabref1 as well as from tabref2 occurs).

Note

In some cases, '*' may be specivied as the field list in the SELECT clause, and an internal table or work area is entered in the INTO clause (instead of a list of fields). If so, the fields are written to the target area from left to right in the order in which the tables appear in the llen in der FROM clause, according to the structure of each table work area. There can be gaps between the table work areas if you use an Alignment Request. For this reason, you should define the target work area with reference to the types of the database tables, as in the following example (not simply by counting the total number of fields).

Example

Example of a JOIN with more than two tables: Select all flights from Frankfurt to New York between September 10th and 20th, 2001 where there are available places, and display the name of the airline.

DATA: BEGIN OF WA,

FLIGHT TYPE SFLIGHT,

PFLI TYPE SPFLI,

CARR TYPE SCARR,

END OF WA.

SELECT * INTO WA

FROM ( SFLIGHT AS F INNER JOIN SPFLI AS P

ON F_{CARRID = P}CARRID AND

F_{CONNID = P}CONNID )

INNER JOIN SCARR AS C

ON F_{CARRID = C}CARRID

WHERE P~CITYFROM = 'FRANKFURT'

AND P~CITYTO = 'NEW YORK'

AND F~FLDATE BETWEEN '20010910' AND '20010920'

AND F_{SEATSOCC < F}SEATSMAX.

WRITE: / WA-CARR-CARRNAME, WA-FLIGHT-FLDATE, WA-FLIGHT-CARRID,

WA-FLIGHT-CONNID.

ENDSELECT.

Re: Joins

Former Member — Thu, 16 Feb 2006 07:02:56 GMT

please go through the below explanation.

Inner join

An inner join essentially finds the intersection between the two tables. This is the most common type of join used, and is considered the default join type. The join example below takes all the records from table A (in this case, employee) and finds the matching record(s) from table B (department). If no match is found, the record from A is not included in the results. If multiple results are found in B that match the predicate then one row will be returned for each (the values from A will be repeated). Special care must be taken when joining tables on columns that can be NULL, since NULL values will never match each other.

Tables:

Table "employee"

LastName DepartmentID

Smith 34

Jones 33

Robinson 34

Jasper 36

Steinberg 33

Rafferty 31

Table "department"

DepartmentName DepartmentID

Sales 31

Engineering 33

Clerical 34

Marketing 35

Example:

SELECT employee.LastName, employee.DepartmentID, department.DepartmentName

FROM employee

INNER JOIN

department

ON employee.DepartmentID = department.DepartmentID

Output:

LastName DepartmentID DepartmentName

Smith 34 Clerical

Jones 33 Engineering

Robinson 34 Clerical

Steinberg 33 Engineering

Rafferty 31 Sales

Left outer join

A left outer join is very different from an inner join. Instead of limiting results to those in both tables, it limits results to those in the "left" table (A). This means that if the ON clause matches 0 records in B, a row in the result will still be returned—but with NULL values for each column from B.

For example, this allows us to find the employee's departments, but still show the employee even when their department is NULL or does not exist.

Example:

SELECT employee.LastName, employee.DepartmentID, department.DepartmentName

FROM employee

LEFT OUTER JOIN

department

ON employee.DepartmentID = department.DepartmentID

output:

LastName DepartmentID DepartmentName

Smith 34 Clerical

Jones 33 Engineering

Robinson 34 Clerical

Jasper 36 NULL

Steinberg 33 Engineering

Rafferty 31 Sales

Right outer join

A right outer join is much like a left outer join, except that the tables are reversed. Every record from the right side, B or department, will be returned, and NULL values will be returned for those that have no matching record in A.

Example:

SELECT employee.LastName, employee.DepartmentID, department.DepartmentName

FROM employee

RIGHT OUTER JOIN

department

ON employee.DepartmentID = department.DepartmentID

output:

LastName DepartmentID DepartmentName

Smith 34 Clerical

Jones 33 Engineering

Robinson 34 Clerical

Steinberg 33 Engineering

Rafferty 31 Sales

NULL 35 Marketing

Hope this will help you.

Regards

Swathi