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SQL: triggers in Oracle
Databases can play an active role in validating and implementing business rules. Through triggers it is possible, in fact. to…
SQL: Recursive CTE
In some scenarios, there is a need to store hierarchies within the database, such as the corporate organizational chart or…
SQL: correlation
In the SQL language, it is possible to condition the execution of a query on the values of the tuples…
SQL: Common Table Expression
Expressing complex queries in SQL language can be really difficult. Dividing the problem into mini-queries is the best strategy to…
SQL: derived tables
In some contexts, it is necessary to compute intermediate results on which we then perform further operations, such as filtering,…
SELECT: set operators
Sometimes we need to operate on the results of several queries as if they were sets. We do not have…
SELECT: NOT IN operator and tuple constructor
In some cases there is a need to exclude one set of values from another set. The SQL language allows…
SELECT: IN operator
In some cases writing SQL queries can be really complex. The divide and conquer strategy, always turns out to be…
SELECT: query with JOIN and GROUP BY
Relational databases are based on modeling that divides the concepts we want to represent into different tables. However, when we…