SQL Server provides the ability to count distinct values across multiple columns in a single query. The `COUNT(DISTINCT)`

function can be used to accomplish this.

Here is an example of counting the distinct combinations of two columns, "column1" and "column2", in a table named "table1":

```
SELECT COUNT(DISTINCT column1, column2)
FROM table1;
```

If you want to count the distinct values of multiple columns separately, you can use multiple `COUNT(DISTINCT)`

statements in the same query, like this:

```
SELECT COUNT(DISTINCT column1) as count1, COUNT(DISTINCT column2) as count2
FROM table1;
```

You can also use the GROUP BY clause to group the results by one or more columns and then count the distinct values within each group. For example:

```
SELECT column1, COUNT(DISTINCT column2)
FROM table1
GROUP BY column1;
```

It's also possible to count distinct values across multiple columns and multiple tables using a join. Here's an example:

```
SELECT COUNT(DISTINCT table1.column1, table2.column2)
FROM table1
JOIN table2 ON table1.id = table2.id;
```

In this example, the query is counting the distinct combinations of "column1" from "table1" and "column2" from "table2", where the "id" column in both tables matches.

It's important to note that when using the `COUNT(DISTINCT)`

function, the result may be less accurate if there are null values in the columns being counted. To exclude null values, you can use the `COUNT(DISTINCT column_name)`

function.

In conclusion, the `COUNT(DISTINCT)`

function in SQL Server can be used to count the number of unique values in multiple columns. You can use it in various ways, such as counting distinct combinations of multiple columns, counting distinct values of multiple columns separately, or counting distinct values across multiple tables using a join.

Another useful function for counting unique values in SQL Server is the `GROUP BY`

clause. This clause allows you to group the results of a query by one or more columns and then perform aggregate functions, such as counting, on the groups. For example, you can use the `GROUP BY`

clause to count the number of unique values in a column and group the results by another column:

```
SELECT column1, COUNT(DISTINCT column2)
FROM table1
GROUP BY column1;
```

In this example, the query is counting the number of unique values in column2 and grouping the results by column1. The result will be a set of rows, one for each unique value of column1, and a count of the number of unique values of column2 that correspond to that value of column1.

You can also use the `GROUP BY`

clause with multiple columns to group the results by multiple columns. For example:

```
SELECT column1, column2, COUNT(DISTINCT column3)
FROM table1
GROUP BY column1, column2;
```

In this example, the query is counting the number of unique values in column3 and grouping the results by column1 and column2. The result will be a set of rows, one for each unique combination of column1 and column2, and a count of the number of unique values of column3 that correspond to that combination.

Another useful function that can be used to count unique values is the `HAVING`

clause. The `HAVING`

clause is used in conjunction with the `GROUP BY`

clause to filter the groups based on a specified condition. For example, you can use the `HAVING`

clause to only show groups that have more than a certain number of unique values:

```
SELECT column1, COUNT(DISTINCT column2)
FROM table1
GROUP BY column1
HAVING COUNT(DISTINCT column2) > 5;
```

In this example, the query is counting the number of unique values in column2 and grouping the results by column1. The `HAVING`

clause is used to only show groups that have more than 5 unique values in column2.

There are also many other aggregate functions that can be used in SQL Server such as SUM, AVG, MIN, MAX etc. These can be useful in combination with `GROUP BY`

and `HAVING`

clause.

In conclusion, there are several ways to count unique values in SQL Server, including using the `COUNT(DISTINCT)`

function, the `GROUP BY`

clause, and the `HAVING`

clause. Each method has its own benefits and use cases and can be used in combination to achieve the desired result.

## Popular questions

- How can I count the distinct combinations of two columns in a table in SQL Server?

Answer: You can use the`COUNT(DISTINCT)`

function to count the distinct combinations of two columns in a table. For example:

```
SELECT COUNT(DISTINCT column1, column2)
FROM table1;
```

- How can I count the distinct values of multiple columns separately in SQL Server?

Answer: You can use multiple`COUNT(DISTINCT)`

statements in the same query, like this:

```
SELECT COUNT(DISTINCT column1) as count1, COUNT(DISTINCT column2) as count2
FROM table1;
```

- How can I use the GROUP BY clause to count the distinct values within each group in SQL Server?

Answer: You can use the GROUP BY clause to group the results by one or more columns and then count the distinct values within each group. For example:

```
SELECT column1, COUNT(DISTINCT column2)
FROM table1
GROUP BY column1;
```

- How can I count distinct values across multiple columns and multiple tables using a join in SQL Server?

Answer: You can use a join to combine data from multiple tables and then use the`COUNT(DISTINCT)`

function to count the distinct values across the columns. For example:

```
SELECT COUNT(DISTINCT table1.column1, table2.column2)
FROM table1
JOIN table2 ON table1.id = table2.id;
```

- How can I exclude null values when using the COUNT(DISTINCT) function in SQL Server?

Answer: To exclude null values when using the`COUNT(DISTINCT)`

function, you can use the`COUNT(DISTINCT column_name)`

function. This will only count the non-null values in the specified column. For example:

```
SELECT COUNT(DISTINCT column1)
FROM table1;
```

This query will only count the distinct non-null values in the column1.

### Tag

Aggregation