PostgreSQL的查询

Question

请帮我查询 下面是桌子和要求的详细信息

Answer 1

您应该使用窗口功能

select alph_letter, alph_group, min(alph_date) OVER (PARTITION BY alph_group) AS min_date from alphabets; 

Answer 2

你可以使用的min开窗变种：

SELECT letter, group, MIN(date) OVER (PARTITION BY group) 
FROM alphabets 

Answer 3

这是另一种方式:)。我使用SQL Server，但语法应该是这个问题类似：

示例数据：

IF OBJECT_ID('tempdb..#Alphabets') IS NOT NULL 
    DROP TABLE #Alphabets; 

CREATE TABLE #Alphabets(Letter VARCHAR(1) 
        , Groups VARCHAR(3) 
        , Dates DATE); 

INSERT INTO #Alphabets 
VALUES 
     ('A' 
    , 'abc' 
    , '20161026'), 
     ('B' 
    , 'abc' 
    , '20161027'), 
     ('C' 
    , 'abc' 
    , '20161028'), 
     ('D' 
    , 'def' 
    , '20161101'), 
     ('E' 
    , 'def' 
    , '20161030'); 

QUERY：

SELECT B.Letter 
    , B.Groups 
    , MinDates 
FROM 
     (SELECT MIN(Dates) AS MinDates 
      , Groups 
     FROM #Alphabets 
     GROUP BY Groups) AS A 
     INNER JOIN #Alphabets AS B ON A.Groups = B.Groups; 

结果：