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Explain mechanism of nested queries?
SQL gives a mechanism for nesting subqueries. A subquery is a select from where expression that is nested within one more query. A common use of sub queries is to perform tests for set membership, make set comparisons, and verify set cardinality.
a) Set membership
(select customer-name
from depositor)
b) Set comparison
select distinct T.branch-name
from branch as T,branch as S
where T.assets > S.assets and S.branch-city='Brooklyn'
a) Test for Empty Relations
Select customer-name
from borrower
where exits (select *
from depositor
where depositor.customername=borrower.customer-name)
a) Test for the Absence of Duplicate Tuples
Create centralized relational database using Top down method- Construction of Logical Model: Translation EERD into Relational Schema: Use the 8 steps algorithm of converting EERD
Gaps in sequence values can happen when: - A rollback happens that is when a statement changes are not accepted. - When the system crashes - When a sequence i
Explain what is DDL? DDL - Data Definition Language: statements used to define the database structure or schema. Some examples: CREATE - to create objects in the database ALT
Give the general form of SQL query? Select A1, A2............., An From R1, R2..............., Rm Where P
Which database object does not physically exist? A view database object does not physically exist.
Explain CNT in the respects of QBE ? CNT: It is one of the aggregation commands given in QBE. It is used to identify number of tuples
Why older data models are being replaced by new data modelling 100 words accepted#
If the insertion violates one or more constraints, then two alternatives are available: Default option: - Insertion can be discarded and the reason of refusal can also be ex
what is query processing?
#question.what is mapping constraints and types?.
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