The DISTINCT keyword in SQL is used to remove duplicate rows from query results. It can be applied to one or more columns in the SELECT statement to return a unique value combination. The usage method is "SELECT DISTINCT column1, column2, ...", the DISTINCT keyword acts on all specified columns. If multiple columns are combined together to produce different results, then these rows will also be considered different and will not be deduplicated.
In SQL, the DISTINCT keyword is used to remove duplicate rows from query results. It can be applied to one or more columns in a SELECT statement to return unique combinations of values.
The usage of DISTINCT is as follows:
SELECT DISTINCT column1, column2, ... FROM table_name;
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The specific explanation is as follows:
- SELECT: Indicates that data is to be selected from the table.
- DISTINCT: Keyword used to identify query results that need to remove duplicate rows.
- column1, column2, ...: Specify the column name to be selected, which can be one or more columns.
For example, suppose there is a table named customers that contains the customer's name and country information. If you want to get a list of unique countries, you can use the following query:
SELECT DISTINCT country FROM customers;
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The above query will return all unique countries in the customers table.
It should be noted that the DISTINCT keyword acts on all specified columns. If multiple columns are combined to produce different results, then these rows will also be considered different and will not be deduplicated.
Summary: In SQL, the DISTINCT keyword is used to remove duplicate rows from query results. It can be applied to one or more columns in a SELECT statement, returning a unique combination of values. By using the DISTINCT keyword, you can get unique result sets.
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