Category: 04. Oracle Clauses
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HAVING Clause
Purpose: The HAVING clause filters results after aggregation, allowing you to specify conditions on grouped records.Syntax Example: Explanation: This retrieves departments where the average salary exceeds 50,000. HAVING is used because the condition is applied after grouping.
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GROUP BY Clause
Purpose: The GROUP BY clause groups rows that have the same values in specified columns into summary rows, often used with aggregate functions.Syntax: Example: Explanation: This counts the number of employees in each department, returning one row per department.
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ORDER BY Clause
Purpose: The ORDER BY clause sorts the result set based on one or more columns, in ascending or descending order.Syntax: Example: Explanation: This sorts the results alphabetically by last_name. The default is ascending order; use DESC for descending.
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WHERE Clause
Purpose: The WHERE clause filters records based on specific conditions, limiting the results to those that meet the criteria.Syntax: Example: Explanation: This retrieves all records from the employees table where the salary exceeds 60,000.
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FROM Clause
Purpose: The FROM clause identifies the table(s) from which to fetch data.Syntax: Example: Explanation: This selects all columns from the departments table. You can also join multiple tables here.
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SELECT Clause
Purpose: The SELECT clause specifies which columns or expressions to retrieve from a database.Syntax: Example: Explanation: This retrieves the first_name and last_name columns from the employees table. You can use * to select all columns.