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Can same column be both primary key and foreign key?
You ‘ll find the answer into this link: Can a database attribute be primary and foreign key? You can create a column having both keys (primary and foreign) but then it will be one to one mapping and add uniqueness to this column.
Can you have a foreign key to the same table?
A foreign key constraint doesn’t have to be linked only to a primary key constraint in another table. FOREIGN KEY constraints can reference another column in the same table, and is referred to as a self-reference. A FOREIGN KEY constraint specified at the column level can list only one reference column.
Is foreign key create index?
MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created. Information about foreign keys on InnoDB tables can also be found in the INNODB_FOREIGN and INNODB_FOREIGN_COLS tables, in the INFORMATION_SCHEMA database.
When to use a FOREIGN KEY constraint in a database?
When you define a foreign key constraint in your database table, an index will not be created automatically on the foreign key columns, as in the PRIMARY KEY constraint situation in which a clustered index will be created automatically when defining it.
When to use foreign key in join criteria?
Changes to PRIMARY KEY constraints are checked with FOREIGN KEY constraints in related tables. Foreign key columns are often used in join criteria when the data from related tables is combined in queries by matching the column (s) in the FOREIGN KEY constraint of one table with the primary or unique key column (s) in the other table.
When to use foreign key columns in SQL Server?
Foreign key columns are often used in join criteria when the data from related tables is combined in queries by matching the column (s) in the FOREIGN KEY constraint of one table with the primary or unique key column (s) in the other table. An index allows Microsoft® SQL Server™ 2000 to find related data in the foreign key table quickly.
Why do I need Index on foreign key columns?
It is highly recommended to create an index on the foreign key columns, to enhance the performance of the joins between the primary and foreign keys, and also reduce the cost of maintaining the relationship between the child and parent tables.