Views vs Inner Join

[Former Member]

Could anyone suggest as to which has a better performance: a view or an internal join? I was asked this question in an interview and went completely blank as I had never worked with any view's... I simply said that I think that a view is better... But would like to know any sound answer & explanation to the same. Thank you....

[Former Member]

Hi

Its more are less same if the view uses 2 tables , because Views also uses table joins between the related tables

but Joins are advantage and more quicker than a view because in View there may be more tables defined so more time.

see the doc on views:

The followings are different types of views:

- Database View (SE11)

Database views are implement an inner join, that is, only records of the primary table (selected via the join operation) for which the corresponding records of the secondary tables also exist are fetched. Inconsistencies between primary and secondary table could, therefore, lead to a reduced selection set.

In database views, the join conditions can be formulated using equality relationships between any base fields. In the other types of view, they must be taken from existing foreign keys. That is, tables can only be collected in a maintenance or help view if they are linked to one another via foreign keys.

- Help View ( SE54)

Help views are used to output additional information when the online help system is called.

When the F4 button is pressed for a screen field, a check is first made on whether a matchcode is defined for this field. If this is not the case, the help view is displayed in which the check table of the field is the primary table. Thus, for each table no more than one help view can be created, that is, a table can only be primary table in at most one help view.

- Projection View

Projection views are used to suppress or mask certain fields in a table (projection), thus minimizing the number of interfaces. This means that only the data that is actually required is exchanged when the database is accessed.

A projection view can draw upon only one table. Selection conditions cannot be specified for projection views.

- Maintenance View ( SE54 )

Maintenance views enable a business-oriented approach to looking at data, while at the same time, making it possible to maintain the data involved. Data from several tables can be summarized in a maintenance view and maintained collectively via this view. That is, the data is entered via the view and then distributed to the underlying tables by the system.

Please have a look at below link. It will help you.

http://help.sap.com/saphelp_nw04/helpdata/en/cf/21ed06446011d189700000e8322d00/frameset.htm

for more detailed info look on:

http://www.sap-img.com/abap/what-is-the-different-types-and-usage-of-views.htm

&

https://www.sdn.sap.com/irj/sdn/wiki?path=/display/home/abap+dictionary&;

JOINS

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

... 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

A

B

C

D

D

E

F

G

H

a1

b1

c1

1

1

e1

f1

g1

h1

a2

b2

c2

1

3

e2

f2

g2

h2

a3

b3

c3

2

4

e3

f3

g3

h3

a4

b4

c4

3

|--|||--|

/

/

/

/

/

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

A

B

C

D

D

E

F

G

H

a1

b1

c1

1

1

e1

f1

g1

h1

a2

b2

c2

1

3

e2

f2

g2

h2

a3

b3

c3

2

4

e3

f3

g3

h3

a4

b4

c4

3

|--|||--|

/

/

/

/

/

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.

reward points if useful

regards

Anji

[Former Member]

Hello Anji,

Couldn't quite get what you meant by, "Its more are less same if the view uses 2 tables , because Views also uses table joins between the related tables

but Joins are advantage and more quicker than a view because in View there may be more tables defined so more time." So do you mean that if we are trying to join only 2 tables then both the views & joins would have the same performance but that the performance of a join is better if we are trying to use more than 2 tables? Don't mind but could you please tell me the reason why the performance of a view suffers at that instant? thanks

[Former Member]

According to SAP recomended coding standard Views are always better than joins when consider the performance issues.