sql 计数_SQL不同，SQL计数不同，SQL选择不同

sql 计数

SQL Distinct keyword is used to select unique set of values for a column in a table.

SQL Distinct关键字用于为表中的列选择唯一的一组值。

SQL不同 (SQL Distinct)

It is very often that we have duplicate data available as part of the data storage. For example, as part of an address table, the state column can have the same value multiple times.通常，我们有重复的数据可作为数据存储的一部分。例如，作为地址表的一部分，状态列可以多次具有相同的值。
In such cases when we need to identify the unique set of values we use SQL DISTINCT keyword along with SELECT to identify the unique values.在这种情况下，当我们需要标识唯一值集时，可以使用SQL DISTINCT关键字和SELECT来标识唯一值。
SQL DISTINCT looks through the list of values and identifies the unique values from the list.SQL DISTINCT浏览值列表，并从列表中识别唯一值。

SQL选择不同的语法 (SQL Select Distinct Syntax)

SELECT DISTINCT column FROM table_name;

In the syntax above the distinct values are retrieved from the column that is mentioned as part of the query.

在上面的语法中，从查询中提到的列中检索不同的值。

Let’s try to understand the DISTINCT command through some example.

让我们尝试通过一些示例来了解DISTINCT命令。

SQL不同的示例 (SQL Distinct Example)

Let us consider the following Customer Table to understand SQL DISTINCT query.

让我们考虑以下客户表，以了解SQL DISTINCT查询。

CustomerId	CustomerName	CustomerAge	CustomerGender
1	John	31	M
2	Amit	25	M
3	Annie	35	F

顾客ID	顾客姓名	客户年龄	客户性别
1个	约翰	31	中号
2	阿米特	25	中号
3	安妮	35	F

Scenario: Identify unique genders from Customer table.

场景：从“客户”表中识别唯一的性别。

Query:

查询：

SELECT DISTINCT CutomerGender FROM Customer;

CustomerGender
M
F

客户性别
中号
F

SQL计数不同的值 (SQL Count Distinct Values)

Sometimes we want to count the total number of distinct values. For example, find out the count of unique gender in the Customer table. Here we will have to use SQL Count function and distinct clauses together within SQL Select statement. We will use the inner select query to first find out the unique gender values and the use count function on it.

有时我们想计算不同值的总数。例如，在“客户”表中查找唯一性别的计数。在这里，我们将必须在SQL Select语句中一起使用SQL Count函数和不同子句。我们将使用内部选择查询来首先找出唯一的性别值及其上的使用计数功能。

SELECT Count(*) As DistinctGender FROM (SELECT DISTINCT CutomerGender FROM Customer);

带计数SQL不同值 (SQL Distinct Values with Count)

What if we want to find the gender and their count in the customer table. We can achieve this using group by clause with distinct clause and count function.

如果我们想在客户表中找到性别及其数量怎么办。我们可以使用带有不同子句和计数功能的group by子句来实现此目的。

SELECT DISTINCT CustomerGender, Count(*) as Occurs FROM Customer GROUP BY CustomerGender;

CustomerGender	Occurs
M	2
F	1

客户性别	发生
中号	2
F	1个

That’s all for SQL Distinct clause with examples. If you are looking for any specific scenario, please comment and I will try to respond with the solution.

这就是带有示例SQL Distinct子句的全部内容。如果您正在寻找任何特定的情况，请发表评论，我将尝试以解决方案做出回应。

翻译自: https://www.journaldev.com/18669/sql-distinct-count-select

sql 计数