无涯教程-PostgreSQL - Distinct语句

PostgreSQL DISTINCT 关键字与SELECT语句结合使用，可消除所有重复记录并仅提取唯一记录。

Distinct - 语法

消除重复记录的DISTINCT关键字的基本语法如下-

SELECT DISTINCT column1, column2,.....columnN
FROM table_name
WHERE [condition]

Distinct - 示例

考虑表 COMPANY 具有以下记录:

# select * from COMPANY;
 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Learnfk |  25 | Texas     |  15000
  3 | Teddy |  23 | Norway    |  20000
  4 | Mark  |  25 | Rich-Mond |  65000
  5 | David |  27 | Texas     |  85000
  6 | Kim   |  22 | South-Hall|  45000
  7 | James |  24 | Houston   |  10000
(7 rows)

让无涯教程向该表中再添加两个记录，如下所示:

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (8, 'Paul', 32, 'California', 20000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (9, 'Learnfk', 25, 'Texas', 15000.00 );

现在，COMPANY表中的记录将是-

 id | name  | age | address    | salary
----+-------+-----+------------+--------
  1 | Paul  |  32 | California |  20000
  2 | Learnfk |  25 | Texas      |  15000
  3 | Teddy |  23 | Norway     |  20000
  4 | Mark  |  25 | Rich-Mond  |  65000
  5 | David |  27 | Texas      |  85000
  6 | Kim   |  22 | South-Hall |  45000
  7 | James |  24 | Houston    |  10000
  8 | Paul  |  32 | California |  20000
  9 | Learnfk |  25 | Texas      |  15000
(9 rows)

首先，让无涯教程看看以下SELECT查询如何返回重复的薪水记录-

testdb=# SELECT name FROM COMPANY;

这将产生以下输出-

 name
-------
 Paul
 Learnfk
 Teddy
 Mark
 David
 Kim
 James
 Paul
 Learnfk
(9 rows)

现在，让无涯教程在上面的SELECT查询中使用 DISTINCT 关键字，然后查看输出-

testdb=# SELECT DISTINCT name FROM COMPANY;

如果无涯教程没有任何重复的条目，这将产生以下输出-

 name
-------
 Teddy
 Paul
 Mark
 David
 Learnfk
 Kim
 James
(7 rows)

参考链接

https://www.learnfk.com/postgresql/postgresql-distinct-keyword.html