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What is NULL? Give an example to described testing for NULL in SQL?
The NULL SQL keyword is used to represent either a missing value or a value which is not applicable in a relational table. Consider there is a relation:
Person(id, name, address, phone)Now to search ids and names of person who do not have a phone is: Select id, name from Person where phone is null
Lossless-Join Decomposition Let us show an intuitive decomposition of a relation. We require a better basis for deciding decompositions since intuition may not always be r
What are the various symbols used to draw an E-R diagram? Explain with the help of an example how weak entity sets are represented in an E-R diagram. Various symbols used to d
Define- relational algebra. The relational algebra is a procedural query language. It having of a set of operations that take one or two relation as input and make a new relati
what do you understand by enhanced entity-relationship
You want to implement following relationships when designing tables. How would you do it? a.) One-to-one b.) One-to-many c.) Many-to-many a.) One-to-One relationship -
Unrepeatable reads : Assume T7 reads X twice during its implementation. If it did not update X itself it could be very disturbing to see a dissimilar value of X in its next read. B
Forward Recovery (Redo): In this system the committed changes made by a transaction are reapplied to a previous copy of the database. In simpler
Multiple column Queries: Syntax: SELECT COLUMN1, COL2,...... FROM TABLE WHERE (COLUMN1, COL2, ...) IN (SELECT COLUMN1, COL2,.... FROM TABLE WHERE );
Super keys of a relation can have extra attributes. Candidate keys are minimal super key, i.e. such a key have no extraneous attribute. An attribute is known as extraneous if even
Aggregation : One limitation of the E-R diagram is that they do not permit representation of relationships between relationships. In such a case the relationship along with its ent
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