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Foreign key is used as a reference in the child table. It is important because it is used to logically relate two and more tables.
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The foreign key uniquely identifies a record in a table T or F?
False. A foreign key is a primary of one table that is in another table. A foreign key can be repeated, so it does not uniquely identify records in the table where it is a foreign key.
What does the term foreign key mean in databases?
The foreign key is used as a reference in a table to the primary key of another table. For example: consider a table employee with id(primary key), name, address,department_id(foreign key) as its fields.Another table department with fields department_id(primary key) and dept_name. So, department_id is primary key in department table and foreign key in employee table.
Why must the primary key of a parent table be determined before the foreign key in the child table?
Because the foreign key is copied from the primary key of the parent table
foreign key?
when a primary key from one table is stored as an attribute of another table
Is foreign key a non key attribute?
a key to a different table
Can a primary key be a foreign key?
If the key is part of a linking table it can be.
Could a table only have one primary key and only one foreign key?
Yes it could. It would have a primary key for its own use and it could then have a foreign linking it to another table. If it is only linked to one other table, then it would only need one foreign key. It is also possible to have the same foreign key linking to more than one table.
When foreign key is used?
A foreign key is when a value of one table, which is a primary key of another table. Manufacturer_table - id - name Models_table - id - manufacturer_id - name Models_table.manufacturer_id should be defined is a foreign key to the Manufacturer_table.id column
Is a foreign key field always on the one side of a one-to-many relationship between two tables?
No. The foreign key is always on the many side. A foreign key is a field that is a primary key in another table, not in the table it is in. It can therefore be repeated in the table it is, so it can act as the many side. In its own table, it is the primary key, and only appears once.
What Foreign key?
In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table. The columns in the referencing table must be the primary key or other candidate key in the referenced table. The values in one row of the referencing columns must occur in a single row in the referenced table. Thus, a row in the referencing table cannot contain values that don't exist in the referenced table (except potentially NULL). This way references can be made to link information together and it is an essential part of database normalization. Multiple rows in the referencing table may refer to the same row in the referenced table. Most of the time, it reflects the one (master table, or referenced table) to many (child table, or referencing table) relationship. The referencing and referenced table may be the same table, i.e. the foreign key refers back to the same table. Such a foreign key is known in SQL:2003 as self-referencing or recursive foreign key. A table may have multiple foreign keys, and each foreign key can have a different referenced table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys. Improper foreign key/primary key relationships or not enforcing those relationships are often the source of many database and data modeling problems.
What is foreign key?
In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table. The columns in the referencing table must be the primary key or other candidate key in the referenced table. The values in one row of the referencing columns must occur in a single row in the referenced table. Thus, a row in the referencing table cannot contain values that don't exist in the referenced table (except potentially NULL). This way references can be made to link information together and it is an essential part of database normalization. Multiple rows in the referencing table may refer to the same row in the referenced table. Most of the time, it reflects the one (master table, or referenced table) to many (child table, or referencing table) relationship. The referencing and referenced table may be the same table, i.e. the foreign key refers back to the same table. Such a foreign key is known in SQL:2003 as self-referencing or recursive foreign key. A table may have multiple foreign keys, and each foreign key can have a different referenced table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys. Improper foreign key/primary key relationships or not enforcing those relationships are often the source of many database and data modeling problems.
What is a foreign key?
In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table. The columns in the referencing table must be the primary key or other candidate key in the referenced table. The values in one row of the referencing columns must occur in a single row in the referenced table. Thus, a row in the referencing table cannot contain values that don't exist in the referenced table (except potentially NULL). This way references can be made to link information together and it is an essential part of database normalization. Multiple rows in the referencing table may refer to the same row in the referenced table. Most of the time, it reflects the one (master table, or referenced table) to many (child table, or referencing table) relationship. The referencing and referenced table may be the same table, i.e. the foreign key refers back to the same table. Such a foreign key is known in SQL:2003 as self-referencing or recursive foreign key. A table may have multiple foreign keys, and each foreign key can have a different referenced table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys. Improper foreign key/primary key relationships or not enforcing those relationships are often the source of many database and data modeling problems.
