sql语句distinct_带DISTINCT子句SQL SELECT语句

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 。

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。
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

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(), 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（）等）一起使用，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

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 。

参考资料 (References)

SQL SELECT DISTINCT — DocumentationSQL SELECT DISTINCT —文档

翻译自: https://www.journaldev.com/41332/sql-select-distinct-statement

sql语句distinct