How we relate two tables using foreign key(fk)?

hi to all,
what are the conditions has to follow to relate two tables.I.e.,
the two tables have same primary keys(pk). if we relate these two tables in one table the pk and fk will be the same then how that table in active.

Hi
To relate two tables..we have foreign key relationship.
In one table v have primary key and in the second table, the same key is foreign key for that table..
To relate two tables, we can use JOINS
If there is already a suitable foreign key between two tables used in the view, these tables can be linked with a join condition from this foreign key.
Create a view on tables TAB1 and TAB2. TAB1 is the primary table of the view. TAB2 is the secondary table of the view. TAB1 is the check table for TAB2. The foreign key fields are assigned to the check table fields as follows:
TAB1-FIELD_A assigned to TAB2-FIELD_1
TAB1-FIELD_A assigned to TAB2-FIELD_1
The join condition of the view generated from the foreign key is then:
CREATE VIEW ... AS SELECT ... WHERE TAB2-FIELD_1 = TAB1-FIELD_A AND TAB2-FIELD_2 = TAB1-FIELD_B.
Join conditions can also be copied from generic and constant foreign keys. If a constant is assigned to a field in the foreign key, it is also assigned to the field in the join condition. There is no join condition for a generic relationship in the foreign key.
The foreign key between tables TAB1 (check table) and TAB2 (foreign key table) is defined as follows:
TAB1-FIELD_A assigned to TAB2-FIELD_1
TAB1-FIELD_B generic
TAB1-FIELD_C assigned to constant C
The join condition for the view generated from the foreign key is in this case:
CREATE VIEW ... AS SELECT ... WHERE TAB2-FIELD_1 = TAB1-FIELD_A AND TAB2-FIELD_2 = C.
Hope it helps
Reward if useful.

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user9005175 wrote:
Hi!
I work on an application wich uses a shopping cart stored in a database. The shopping cart uses two tables:
CART: Holds information common for one shopping cart: the user it is connected to etc.
- Primary key: CART_ID
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A while ago we added indexes, both on ROW_ID and on PARENT_ID. Could the index on PARENT_ID have been harmful, since there is no foreign key?
Index on parent_id would only be harmful if you do not make use of index after creating it (i.e. there is no query which make use of this index).
And if you decide to have a foreign key on parent_id then I suggest to have index too on parent_id as it would be helpful atleast when you delete any record in this table.
Best regards!

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Let me elaborate on my problem
TAB1
=====
a1 b1 c1
a2 b2 c2
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=====
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x3 y3 z3 a3
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p3 q3 r3 y3
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Edited by: user9974355 on Dec 18, 2008 12:00 AM

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Regards,

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http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14200/queries006.htm#i2054062
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Would describe type of joins in ABAP, which might differ with other joins.
The join syntax represents a recursively nestable join expression. A join expression consists of a left-hand and a right- hand side, which are joined either by means of INNER JOIN or LEFT OUTER JOIN. Depending on the type of join, a join expression can be either an inner (INNER) or an outer (LEFT OUTER) join. Every join expression can be enclosed in round brackets. If a join expression is used, the SELECT command circumvents SAP buffering.
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AS can be used to specify an alternative table name tabalias for each of the specified database table names or for every view. A database table or a view can occur multiple times within a join expression and, in this case, have various alternative names.
The syntax of the join conditions join_cond is the same as that of the sql_cond conditions after the addition WHERE, with the following differences:
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Individual comparisons may be joined using AND only.
All comparisons must contain a column in the database table or the view dbtab_right on the right-hand side as an operand.
The following additions not be used: NOT, LIKE, IN.
No sub-queries may be used.
For outer joins, only equality comparisons (=, EQ) are possible.
If an outer join occurs after FROM, the join condition of every join expression must contain at least one comparison between columns on the left-hand and the right-hand side.
In outer joins, all comparisons that contain columns as operands in the database table or the view dbtab_right on the right-hand side must be specified in the corresponding join condition. In the WHERE condition of the same SELECT command, these columns are not allowed as operands.
Resulting set for inner join
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Resulting set for outer join
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Note
If the same column name occurs in several database tables in a join expression, they have to be identified in all remaining additions of the SELECT statement by using the column selector ~.
Example
Join the columns carrname, connid, fldate of the database tables scarr, spfli and sflight by means of two inner joins. A list is created of the flights from p_cityfr to p_cityto. Alternative names are used for every table.
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connid TYPE spfli-connid,
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FROM ( ( scarr AS c
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AND p~cityfrom = p_cityfr
AND p~cityto = p_cityto )
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Example
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carrname TYPE scarr-carrname,
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WITH NON-UNIQUE KEY carrid.
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INTO CORRESPONDING FIELDS OF TABLE itab
FROM scarr AS s
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LOOP AT itab INTO wa.
IF wa-connid = '0000'.
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ENDIF.
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Re: Unable to insert a new row with a sequence generated column id
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Hi Sreenivas,
> Is it possible to update two tables using the Update Statement without using Stored Procedures.
Yes its possible through join statement
Check this links
Update in JDBC Sender adapter for more than one table
data from 2 tables for jdbc sender adapter
Regards
Ramesh

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ok i have checked that for the past few days but its not what i want.
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Not use foreign keys.

I would like to know if is it bad if I don't want to use foreign keys? is it just a constraint? Is it useful? If I wont use delete on cascade for example is it mandatory to use foreign keys? Please help me with this doubt.
Thanks.

A Small example:
DROP TABLE T_TABLES ;
CREATE TABLE T_TABLES AS
SELECT ROWNUM AS ID, OWNER, TABLE_NAME
FROM   ALL_TABLES;
ALTER TABLE T_TABLES ADD CONSTRAINTS PK_TABLES PRIMARY KEY(ID);
DROP TABLE T_TABLE_COLUMNS ;
CREATE TABLE T_TABLE_COLUMNS AS
SELECT T.ID, TC.OWNER, TC.TABLE_NAME, TC.COLUMN_NAME, TC.DATA_TYPE
FROM   ALL_TAB_COLS TC
           JOIN T_TABLES T ON (T.OWNER = TC.OWNER AND T.TABLE_NAME = TC.TABLE_NAME)
WHERE T.TABLE_NAME NOT IN ('T_TABLES', 'T_TABLE_COLUMNS'); -- EXCEPT THESE TWO TABLES
EXPLAIN PLAN FOR
SELECT *
FROM   T_TABLE_COLUMNS
WHERE ID IN (SELECT ID FROM T_TABLES);
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
| Id | Operation          | Name            | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |                 | 27823 | 3586K|    63   (7)| 00:00:01 |
|   1 | NESTED LOOPS      |                 | 27823 | 3586K|    63   (7)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| T_TABLE_COLUMNS | 27823 | 3233K|    60   (2)| 00:00:01 |
|* 3 |   INDEX UNIQUE SCAN| PK_TABLES       |     1 |    13 |     0   (0)| 00:00:01 |
--ADD FOREIGN KEY
ALTER TABLE T_TABLE_COLUMNS ADD CONSTRAINT FK_TABLES FOREIGN KEY(ID) REFERENCES T_TABLES(ID);
-- SAME QUERY AGAIN
EXPLAIN PLAN FOR
SELECT *
FROM   T_TABLE_COLUMNS
WHERE ID IN (SELECT ID FROM T_TABLES);
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
-- NO JOIN ANYMORE
| Id | Operation         | Name            | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |                 | 27823 | 3233K|    60   (2)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T_TABLE_COLUMNS | 27823 | 3233K|    60   (2)| 00:00:01 |
-------------------------------------------------------------------------------------FKs can even save you from joins.

How we relate two tables using foreign key(fk)?

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