Question

我正在用Rails编写查询。我有名为School and Skill的表格。技能有专栏

id: integer
name: text 
school_id: integer

我有@skills，其中包含一些行。但是@skills可以有重复的名称。

我想从@skills中删除重复的行，其中school_id == 1。

例如，如果@skills返回


#<ActiveRecord::Relation [#<Skill id: 249, name: "3 D Priniting", school_id: 1>, 
  #<Skill id: 258, name: "Cinematography", school_id: 11>,
  #<Skill id: 174, name: "Sports", school_id: 1>, 
  #<Skill id: 259, name: "Cinematography", school_id: 1>, 
  #<Skill id: 300, name: "Sales", school_id: 11>, 
  #<Skill id: 301, name: "Marketing", school_id: 11>,]

此处的技能ID 258和259具有相同的名称。所以我想删除259，因为它具有school_id == 1。

我使用了以下SQL查询，但是它选择了MIN（id）。

SELECT MIN(id) as id, school_id 
FROM `skills` 
GROUP BY `skills`.`tag_id`,  
`skills`.`tag_type`, `skills`.`school_id`, `skills`.`master_tag_id`

我可以这样删除重复项吗？我想在一个查询中完成此操作。

注意：感谢ActiveRecord中的解决方案。

Answer 1

您可以尝试以下查询：

set @lagName := '';
set @rn := 0;
select id, name, school_id from (
  select 
    case when @lagName = name then @rn:=@rn+1 else @rn:=1 end rn,
    @lagName:=name,
    id,
    name,
    school_id
  from Skills
  order by name, school_id desc
) a where rn=1

它根据name列在组内使用行编号。每个组然后按school_id进行排序，因此school_id排在最后。然后选择rn等于1的那些记录就足够了。

Answer 2

import pygame

black = (0,0,0)
white = (255,255,255)
gray  = (128,128,128)
red   = (255,0,0)

pygame.init()
gameDisplay = pygame.display.set_mode( (800,600))
clock = pygame.time.Clock()

def button(msg,x,y,w,h,ic,ac,action=None):
    mouse = pygame.mouse.get_pos()
    click = pygame.mouse.get_pressed()

    if x+w > mouse[0] > x and y+h > mouse[1] > y:
        pygame.draw.rect(gameDisplay, ac, (x,y,w,h))
        if click[0] == 1 and action != None:
            action()         
    else:
        pygame.draw.rect(gameDisplay, ic, (x,y,w,h))

    smallText = pygame.font.SysFont("comicsansms",20)
    textSurf = smallText.render(msg, True, red)
    textRect = textSurf.get_rect()
    textRect.center = ( (x+(w/2)), (y+(h/2)) )
    gameDisplay.blit(textSurf, textRect)

def change_draw_to_intro():
    global draw
    draw = draw_intro

def change_draw_to_other():
    global draw
    draw = draw_other

def change_draw_to_BE01():
    global draw
    draw = draw_BE01

def draw_BE01():
    gameDisplay.fill(white)
    #gameDisplay.blit(BE01Img,(0,0))
    button("BACK",350,450,100,50,black,gray,change_draw_to_intro)

def draw_intro():
    gameDisplay.fill(white)
    #gameDisplay.blit(introImg,(0,0))
    button("START",350,450,100,50,black,gray,change_draw_to_other)

def draw_other():
    gameDisplay.fill(white)
    #gameDisplay.blit(scene01Img,(0,0))
    button("1",200,450,100,50,black,gray,change_draw_to_BE01)

def quitgame():
    pygame.quit()
    quit()   

def game_loop():
    global draw

    draw = draw_intro

    gameExit = False

    while not gameExit:

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()

        draw()

        pygame.display.update()
        clock.tick(60)

game_loop()
pygame.quit()
quit()

Answer 3

使用子查询方法。第一组@skills表使用Schol_id和名称。然后执行实际的选择语句。

select * from skills where id in (select id from skills group by school_id, name);

是否存在基于mysql中的条件从集合中删除重复项的查询？

3 个答案: