1. SELECT DISTINCT ON的用途 SELECT DISTINCT ON用于在一组重复的记录中选取每个分组的第一条记录。它允许你指定某些列用于区分唯一性,并且可以返回每个分组中的任意字段,而不像GROUP BY那样局限于只能查询和排序用于分组的字段。 2. SELECT DISTINCT ON的基本语法结构 ...
1) PostgreSQL SELECT DISTINCT one column example The following statement selects unique values from the bcolor column of the t1 table and sorts the result set in alphabetical order by using the ORDER BY clause. SELECT DISTINCT bcolor FROM colors ORDER BY bcolor; Output: bcolor --- blue gre...
# SELECT DISTINCT ON (code) code, id, name from test_dist; code | id | name ---+---+--- 1 | 1 | a 2 | 4 | m 3 | 6 | j 4 | 8 | j (4 rows) 这里,根据code去重,id和name随机取出,这样可以获得code维度的数据。如果不去重,获得原始数据,code有重复。 本文参与 腾讯云自媒体同步...
有时候我们需要同时使用SELECT DISTINCT和SUBSTRING函数来进行更复杂的文本操作。在本例中,我们将使用这两个函数来实现对每个resource_version字段值的前3个字符进行去重查询。 SELECT DISTINCT substring(resource_version,0, position(split_part(resource_version,'.',4)inresource_version)-1) FROM tb_resource; 以上...
(Instead of DISTINCT the key word ALL can be used to specify the default behavior of retaining all rows.) Obviously, two rows are considered distinct if they differ in at least one column value. Null values are considered equal in this comparison. 2、返回指定列唯一的任意行。 也可以使用...
PostgreSQL has a really interesting and powerful construct calledSELECT DISTINCT ON. No, this is not a typicalDISTINCT. This is different. It is perfect when you have groups of data that are similar and want to pull a single record out of each group, based on a specific ordering. ...
function_call[AS]alias (column_definition[, ... ]) function_call AS[alias](column_definition[, ... ]) ROWSFROM( ... function_call AS (column_definition[, ... ])[, ... ]) 例子: SELECT * FROM ROWS FROM (json_to_recordset('[{"a":40,"b":"foo"},{"a":"100","b":"bar"...
例如,我们查看下 select 语句的语法:postgres=# \help SELECT Command: SELECT Description: retrieve rows from a table or view Syntax: [ WITH [ RECURSIVE ] with_query [, ...] ] SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ] [ * | expression [ [ AS ] output_name ] [...
1. SELECT DISTINCT语句 SELECT DISTINCT语句用于从表中选择不重复的记录。如果没有指定列名,则会选择所有列。在本例中,我们将使用SELECT DISTINCT语句来选择去重后的resource_version字段值。 SELECT DISTINCT resource_version FROM tb_resource; 2. SUBSTRING函数 SUBSTRING函数用于从字符串中提取子串。它有三个参数:...
在PostgreSQL中,我们可以使用SELECT DISTINCT和SUBSTRING函数来实现对某个字段进行去重查询。本文将介绍如何使用这两个函数来实现对resource_version字段的去重查询。 1.SELECT DISTINCT语句 SELECT DISTINCT语句用于从表中选择不重复的记录。如果没有指定列名,则会选择所有列。在本例中,我们将使用SELECT DISTINCT语句来选择去...