NOT IN and NULL: a dangerous combination
Non-correlated subqueries (where the inner query does not have any column from the outer query tables) are usually implemented using[…]
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Tag: SQL
Using SQL in Python
Python has become one of the most popular programming languages and is used in various contexts, including in WEB applications[…]
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LEAD and LAG: accessing multiple rows without self join
LEAD and LAG are window functions that enable the simultaneous access to a table’s row and to other row related[…]
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Coalesce, NVL, ISNULL, Case, … What should a I use?
There are a lot of options to use when testing for NULL values in SQL. One should use built-in functions[…]
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Looking for missing values using recursive queries
In most of application databases, we can find one or more numeric columns representing IDs or used as primary keys.[…]
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Are ROWNUM and ROWID the same column?
No. In Oracle DBMS, ROWNUM and ROWID are pseudocolumns that can be accessed in SQL queries, but they aren’t the[…]
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Using a recursive query to create a list of dates
In enterprise database systems, one may commonly find business events (e.g. sales, revenue, etc) associated to dates or months. In[…]
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Filtering data in SQL using Where and Having
The Where clause is one of the mostly commonly used clauses in the SQL language. On the other hand, the[…]
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