How to use sql distinct

The DISTINCT operator is used to exclude duplicate rows in SQL queries and returns only unique values. It is suitable for scenarios such as obtaining a list of unique values, counting the number of unique values, and using it in combination with GROUP BY.

Usage of DISTINCT in SQL

The DISTINCT operator is used to exclude duplicate rows from SQL query results and returns only unique values. It is used to ensure that the result set does not contain any duplicate data.

grammar

 <code>SELECT DISTINCT column_name(s) FROM table_name;</code>

in:

• column_name(s) : Specifies the column to which to perform a DISTINCT operation. Multiple columns can be specified.
• table_name : The data table to query.

usage

Common scenarios for using the DISTINCT operator include:

• Get a list of unique values ​​in the table:

   <code>SELECT DISTINCT name FROM employees;</code>

• The number of unique values ​​is counted:

   <code>SELECT COUNT(DISTINCT name) FROM employees;</code>

• Use in combination with GROUP BY:
  DISTINCT can be used with GROUP BY to group and count unique values ​​under specific conditions.

   <code>SELECT department, COUNT(DISTINCT employee_id) FROM employees GROUP BY department;</code>

Things to note

• The DISTINCT operator can only be used in SELECT statements.
• If DISTINCT is used in a column, the values ​​in other columns are also excluded, even if they are not repeated.
• The DISTINCT operator may affect query performance on large datasets because it requires additional sorting and comparison steps.

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