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What is a foreign key, and what is it used for?
A foreign key is used to establish relationships between relations in the relational model. Technically, a foreign key is a column (or columns) appearing in one relation that is (are) the primary key of another table. Although there might be exceptions, the values in the foreign key columns usually must correspond to values existing in the set of primary key values. This correspondence necessity is created in a database using a referential integrity constraint on the foreign key.
What is a primary key? Primary key is chosen by the database designer as the principal means of identifying an entity in the entity set.
Introduction In large projects, we can have many different companies working together. Generally, the project or contract is awarded to one company (Principal Contractor), which
Answer SQL Queries to extract data from data tables and questions on mapping conceptual data models into relational data model.
The traffic data mgmt. systems infrastructure plan describes the software, hardware, data network, and other elements that will support the TDMS. The infrastructure plan is based o
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Give the forms of triggers? The triggering event can be insert or delete. For updated the trigger can state columns. The referencing old row as clause The referencing
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example of embedded SQL query
The entity type STUDENT has the following attributes: Student Name, Address, Phone, Age, Activity, and No of Years. Activity represents some campus-based student activity, and No o
When It is better to use files than a DBMS? It is better to use files than a DBMS when Multiple users wish to access the data.
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