Скачать или смотреть How to use Count function in SQL | Aggregate functions | Data Analyst Interview Questions

The SQL COUNT DISTINCT function is used to return the number of unique values in a specified column or set of columns in a table. The syntax for the COUNT DISTINCT function is:

SELECT COUNT(DISTINCT column_name)
FROM table_name;

Here, column_name is the name of the column or columns you want to count the distinct values of, and table_name is the name of the table you want to query.

Note that the COUNT DISTINCT function only counts the number of unique values in a column or set of columns. If you want to count the total number of rows in a table that meet certain conditions, you should use the regular COUNT function instead.
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