sql语句distinct_带DISTINCT子句SQL SELECT语句

爱被打了一巴掌 2023-02-28 06:14 18阅读 0赞

sql语句distinct

Hey, folks! In this article, we will we focusing on **SQL SELECT DISTINCT statement**.

嘿伙计！ 在本文中，我们将重点介绍**SQL SELECT DISTINCT语句** 。

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## 什么是SQL SELECT语句？ **(****What is SQL SELECT statement?****)** ##

[SQL Select statement][] is used to select and display particular data from the column of a table/database.

[SQL Select语句][SQL Select statement]用于从表/数据库的列中选择和显示特定数据。

**Syntax:**

**句法：**

SELECT * FROM Table-name;
    OR
    SELECT column1, column2, ...., columnN from Table-name;

**Example:**

**例：**

create table Info(id integer, Cost integer, city varchar(200));
    insert into Info(id, Cost,city) values(1, 100,"Pune");
    insert into Info(id, Cost,city) values(2, 50, "Satara");
    insert into Info(id, Cost,city) values(3, 65,"Pune");
    insert into Info(id, Cost,city) values(4, 97,"Mumbai");
    insert into Info(id, Cost,city) values(5, 12,"USA");
    Select * from Info;

**Output:**

**输出：**

id	Cost	city
    1	100	Pune
    2	50	Satara
    3	65	Pune
    4	97	Mumbai
    5	12	USA

--------------------

## 什么是SQL DISTINCT子句？ **(****What is SQL DISTINCT Clause?****)** ##

[SQL DISTINCT clause][] helps extract the non-redundant values from the table i.e. **it excludes the redundant/repeated values and displays only the unique values**.

[SQL DISTINCT子句][SQL DISTINCT clause]有助于从表中提取非冗余值，即**它排除了冗余/重复值，并且仅显示唯一值** 。

*  DISTINCT clause works well with [SQL Aggregation functions][].
    
    DISTINCT子句与[SQL Aggregation函数配合良好][SQL Aggregation functions] 。
 *  Multiple columns cannot be mapped at once by SQL DISTINCT clause.
    
    SQL DISTINCT子句不能一次映射多个列。

**Syntax:**

**句法：**

DISTINCT(column-name)

**Example:**

**例：**

SELECT DISTINCT(city) from Info;

**Output:**

**输出：**

city
    Pune
    Satara
    Mumbai
    USA

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## 使用DISTINCT子句SQL SELECT的工作 **(****Working of SQL SELECT with DISTINCT clause****)** ##

`SQL SELECT statement` can be clubbed along with `DISTINCT clause` to extract and display the unique values from a particular table.

可以将`SQL SELECT statement`与`DISTINCT clause`在一起，以提取和显示特定表中的唯一值。

Moreover, the SELECT DISTINCT statement can be used along with different aggregation functions such as [COUNT(), AVG()][COUNT_ AVG], etc to display the unique values according to certain predefined conditions.

此外，SELECT DISTINCT语句可以与不同的聚合函数（例如[COUNT（），AVG（）][COUNT_ AVG]等[）一起使用][COUNT_ AVG] ，以根据某些预定义条件显示唯一值。

**Syntax:**

**句法：**

SELECT DISTINCT(column-name)
    FROM Table;

Having understood the working of SQL SELECT DISTINCT statement, let us now have a look at the implementation of the same in the below section.

了解了SQL SELECT DISTINCT语句的工作原理之后，现在让我们在下面的部分中了解一下该语句的实现。

--------------------

## 通过示例实现SQL SELECT DISTINCT **(****Implementing SQL SELECT DISTINCT through examples****)** ##

In the below example, we have clubbed SQL DISTINCT statement along with [ORDER BY clause][]. Wherein, it displays the unique ‘city’ data in an ascending order according to the Cost values.

在下面的示例中，我们将SQL DISTINCT语句与[ORDER BY子句][ORDER BY clause]结合在一起。 其中，它将根据“成本”值以升序显示唯一的“城市”数据。

Select DISTINCT(city),Cost
    From Info
    ORDER BY Cost;

**Output:**

**输出：**

city	Cost
    USA	12
    Satara	50
    Pune	65
    Mumbai	97
    Pune	100

Now, we have used `COUNT(*) function`along with SELECT DISTINCT statement to display the count of all the unique values of the column — ‘city’.

现在，我们已经使用`COUNT(*) function`和SELECT DISTINCT语句来显示列“ city”的所有唯一值的计数。

SELECT COUNT(*) 
    FROM (
    SELECT  DISTINCT city
    FROM Info) as Inn;

**Output:**

**输出：**

COUNT(*)
    4

Here, we have created a Table — ‘Info’ with various columns. Further, we have used SELECT DISTINCT statement along with [WHERE clause][] to extract and display the unique values whose ‘Cost’ is equal to 100.

在这里，我们用不同的列创建了一个表-'Info'。 此外，我们将SELECT DISTINCT语句与[WHERE子句][WHERE clause]一起使用，以提取并显示“成本”等于100的唯一值。

create table Info(id integer, Cost integer, city varchar(200));
    insert into Info(id, Cost,city) values(1, 100,"Pune");
    insert into Info(id, Cost,city) values(2, 50, "Satara");
    insert into Info(id, Cost,city) values(3, 100,"Pune");
    insert into Info(id, Cost,city) values(4, 100,"Mumbai");
    insert into Info(id, Cost,city) values(5, 12,"USA");
    SELECT DISTINCT city,Cost
    FROM Info 
    WHERE Cost=100;

**Output:**

**输出：**

city	Cost
    Pune	100
    Mumbai	100

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## 结论 **(****Conclusion****)** ##

By this, we have come to the end of this topic. Feel free to comment below in case you come across any doubt.

至此，我们到了本主题的结尾。 如果您有任何疑问，请在下面发表评论。

For more such topics related to SQL, please do visit [SQL JournalDev][].

有关与SQL有关的更多此类主题，请访问[SQL JournalDev][] 。

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## 参考资料 **(****References****)** ##

*  [SQL SELECT DISTINCT — Documentation][SQL SELECT DISTINCT _ Documentation]
    
    [SQL SELECT DISTINCT —文档][SQL SELECT DISTINCT _ Documentation]

> 翻译自: [https://www.journaldev.com/41332/sql-select-distinct-statement][https_www.journaldev.com_41332_sql-select-distinct-statement]

sql语句distinct

[SQL Select statement]: https://www.journaldev.com/18262/sql-select
[SQL DISTINCT clause]: https://www.journaldev.com/18669/sql-distinct-count-select
[SQL Aggregation functions]: https://www.journaldev.com/34288/sql-aggregate-functions
[COUNT_ AVG]: https://www.journaldev.com/40669/sql-sum-avg-count
[ORDER BY clause]: https://www.journaldev.com/18675/sql-order-by-clause
[WHERE clause]: https://www.journaldev.com/18411/sql-where-clause
[SQL JournalDev]: https://www.journaldev.com/sql
[SQL SELECT DISTINCT _ Documentation]: https://docs.microsoft.com/en-us/sql/dmx/select-distinct-from-model-dmx?view=sqlallproducts-allversions
[https_www.journaldev.com_41332_sql-select-distinct-statement]: https://www.journaldev.com/41332/sql-select-distinct-statement