A query which uses values from the outer query is called as a correlated sub query. The subquery is executed once and uses the results for all the evaluations in the outer query.

Example:

Here, the sub query references the employee_id in outer query. The value of the employee_id changes by row of the outer query, so the database must rerun the subquery for each row comparison. The outer query knows nothing about the inner query except its results.

select employee_id, appraisal_id, appraisal_amount From employee
where
appraisal_amount < (select max(appraisal_amount)
from employee e
where employee_id = e. employee_id);

Oracle Backup and Recovery

What is configure command and recovery catalog?, What are different types of backup? (Hot, Cold, logical, Physical)?, Whats the Concept of Flashback Query in Oracle (10g in particular) and how is it beneficial?...............

Oracle replication

Read only replication creates local copy of table data originating from one or more remote master tables. An application can query the data in a read-only table snapshot..............

Oracle transaction

The parser scans the statement and breaks it into logical units such as keywords, identifiers and operators, A query or a sequence tree is built using the units above. This is done to transform the source data into the format required by the result set.............

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UNION: The UNION operator is used to combine the result-set of two or more SELECT statements Tables of both the select statement must have the same number of columns with similar data types. It eliminates duplicates..........

What is a SNAPSHOT LOG?

A snapshot log is a copy of the master table. The snapshot table is updated using batch updates, The log can also be used to track the rows that have been updated in the master table........