How to remove duplicates in oracle

Oracle is a popular relational database system whose operators and functions can be used to handle duplicate data. Frequently used functions include DISTINCT, GROUP BY, HAVING and UNION, etc. In this article, we will discuss ways to remove duplicate records in Oracle.

Method 1: Use the DISTINCT keyword
The DISTINCT keyword is used to return unique data rows. Using this keyword, you can quickly retrieve different values ​​from the table. For example, if you want to get a unique city from the table, you can use the following SQL statement:

SELECT DISTINCT(city) FROM customers

The result will return a list of unique cities in the table.

Method 2: Use the GROUP BY keyword
The GROUP BY keyword is similar to the DISTINCT keyword, but it can group the results according to the specified column. For example, we may need to group customers by country. The following SQL statement will return a list of customers in each country:

SELECT country, COUNT(*) FROM customers GROUP BY country

The result will return a table containing the number of customers in each country.

Method 3: Use the HAVING clause
The HAVING clause is used to filter the GROUP BY results. For example, we might need to retrieve the countries where the number of customers is greater than 10 in each country. The following SQL statement can achieve this purpose:

SELECT country, COUNT() FROM customers GROUP BY country HAVING COUNT() > 10

The result will return the number of customers greater than List of 10 countries.

Method 4: Use the UNION keyword
The UNION keyword is used to combine the result sets of two or more SELECT statements. For example, we may need to combine records from two tables but don't want to have duplicate records. The following SQL statement can achieve this purpose:

SELECT column1, column2 FROM table1
UNION
SELECT column1, column2 FROM table2

The result will return the only records in the two tables.

Method 5: Use the INTERSECT keyword
INTERSECT keyword is used to obtain the common results of two SELECT statements. For example, we may need to get all matching data from two tables. The following SQL statements can achieve this purpose:

SELECT column1, column2 FROM table1
INTERSECT
SELECT column1, column2 FROM table2

The above are several methods for Oracle to remove duplicate records. During data management and data analysis, these tips can help you work and query data more efficiently.

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