The difference between having and where in oracle

The difference between HAVING and WHERE clauses is that HAVING is used to filter aggregate results (that is, grouped data), while WHERE is used to filter rows in the base table or view. Additionally, HAVING requires the data to be grouped, while WHERE does not.

The difference between HAVING and WHERE clauses in Oracle

Introduction
HAVING and WHERE are two clauses used in Oracle to filter data results. Although they all have similar purposes, they have different application scenarios and functions.

Application scenarios

• WHERE clause: Filter rows in the base table or view.
• HAVING clause: Filter the results of aggregate functions (such as SUM, COUNT), usually used to filter grouped data.

Grammar
WHERE clause:

<code>SELECT column(s) FROM table WHERE condition(s)</code>

HAVING clause:

<code>SELECT column(s)
FROM table
GROUP BY column(s)
HAVING condition(s)</code>

Function comparison

##FeaturesWHERE clauseHAVING clauseFunctionFilter rowsFilter aggregate resultsUsage scenariosBasic table or viewGrouped dataOperation timingBefore data retrievalAfter data aggregationMust be groupedNot requiredRequiredComparison operatorSupportedNot supported (only aggregate functions are supported)

Example

WHERE clause example:

<code>SELECT * FROM customers WHERE country = 'USA';</code>

This query retrieves all customers from the United States.

HAVING clause example:

<code>SELECT country, COUNT(*) AS customer_count
FROM customers
GROUP BY country
HAVING customer_count > 1000;</code>

This query groups the number of customers in each country and retrieves countries with more than 1000 customers.

Conclusion

HAVING and WHERE clauses are used to filter data in Oracle, but their functions are different and their application scenarios are also different. The WHERE clause is used to filter the underlying data, while the HAVING clause is used to filter the aggregated data.

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