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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…
SELECT: simple query structure
The SELECT statement in the SQL language is perhaps the most widely used as it allows us to retrieve information…
SQL: transactions and data manipulation
Databases provide a great tool for storing large masses of data. But how do we write the data correctly into…