Question

我有以下查询

string sql =
          "IF NOT EXISTS(SELECT testId from TestData where testId=@testId) " +
          "Insert INTO TestData (testId, jsonString) VALUES(@testId, @jsonstring) " +
          "else " +
          "UPDATE TestData SET jsonString=@jsonstring WHERE testId=@testId " +
          "SELECT CAST(scope_identity() AS int)";

为了使TestData表中的一行（如果不存在则创建）或者更新（如果不存在）。

我第一次使用它时，所以当记录不存在时，它可以正常工作。如果我再次调用该函数：

conn.Open();
newID = (Int32)cmd.ExecuteScalar();

所以这次记录已经存在，我在尝试转换为Int32时可能会出现转换错误。

我的查询是否有问题，我该怎么做才能解决这个问题？

Answer 1

错误可能是因为你已经有了testid.scope_identity（）将返回null，因为它做了任何身份操作。使用选择@testId进行更新。

Answer 2

据推测，您需要更像这样的代码：

import pygame

# --- constants ---

BLACK = (  0,  0,  0)
RED   = (255,  0,  0)

# --- classes ---

class Label():

    def __init__(self, text, x, y, width):

        font = pygame.font.SysFont(None, 35)

        # generate full image
        self.image = font.render(text, True, RED)
        self.rect = self.image.get_rect(x=x, y=y)

        self.width = width
        self.speed = 1

        # offset of visible part
        self.offset_x = 0
        self.max_offset_x = self.rect.width - self.width

        # visible part of image as 'rect' - 'width' is always the same
        self.sub_image_rect = self.image.get_rect(x=0, width=self.width) # changed

    def move(self):

        # change offset
        self.offset_x += self.speed

        # change move direction
        if self.offset_x < 0:
            self.offset_x = 0
            self.speed = -self.speed
        elif self.offset_x > self.max_offset_x:
            self.offset_x = self.max_offset_x
            self.speed = -self.speed

        # visible part of image - change only `x` 
        self.sub_image_rect.x = self.offset_x  # changed

    def draw(self, surface):
        surface.blit(self.image, self.rect, area=self.sub_image_rect)  # changed

# --- main ---

pygame.init()
screen = pygame.display.set_mode((800,600))

label = Label("Hello World of Python and Pygame!", 100, 100, 200)

# --- mainloop ---

fps = pygame.time.Clock()
running = True

while running:

    # --- events ---

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN:
            if event.key ==  pygame.K_ESCAPE:
                running = False

    # --- updates ---

    label.move()

    # --- draws ---

    screen.fill(BLACK)

    label.draw(screen)

    fps.tick(25)
    pygame.display.flip()

# --- the end ---

pygame.quit()

我假设IF NOT EXISTS (SELECT 1 from TestData where testId = @testId) BEGIN Insert INTO TestData(testId, jsonString) VALUES(@testId, @jsonstring); SELECT CAST(scope_identity() AS int); END ELSE BEGIN UPDATE TestData SET jsonString = @jsonstring WHERE testId = @testId; SELECT CAST(id as int) FROM TestData WHERE testId = @testId; END;以外的某些列是标识列 - 比如说testId。通常，您不会在id语句中设置标识列。

此外，insert可能适用于您的目的。但是从新行返回信息的最安全方法是使用scope_identity()子句（请参阅here）。

sql查询返回的转换值出错

2 个答案: