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constraints

MySQL 错误:无法添加外键约束?(MySQL error: Cannot add foreign key constraint?)

问题 创建最后一个表时总是出现错误: “无法添加外键约束” 。 系统:Mac OS X 10.9 数据库:MySQL 5.6.14 DBM : 续集专业版 CREATE TABLE users ( uid INT AUTO_INCREMENT PRIMARY KEY, uname VARCHAR(20) NOT NULL, uemail VARCHAR(20) NOT NULL, ucity VARCHAR(20), upassw VARCHAR(20) NOT NULL ); CREATE TABLE songs( sid INT AUTO_INCREMENT PRIMARY KEY, sname VARCHAR(20) NOT NULL, srldate DATE NOT NULL ); CREATE TABLE albums ( albid INT AUTO_INCREMENT PRIMARY KEY, albname VARCHAR(20) NOT NULL, albrldate DATE NOT NULL, albrltime TIME NOT NULL ); CREATE TABLE artists ( aid INT AUTO_INCREMENT PRIMARY KEY, aname VARCHAR(20) NOT NULL ); CREATE TABLE

2021-09-25 03:06:04    分类:技术分享    mysql   sql   foreign-keys   constraints   mysql-error-1064

MySQL 错误:无法添加外键约束?(MySQL error: Cannot add foreign key constraint?)

问题 创建最后一个表时总是出现错误: “无法添加外键约束” 。 系统:Mac OS X 10.9 数据库:MySQL 5.6.14 DBM : 续集专业版 CREATE TABLE users ( uid INT AUTO_INCREMENT PRIMARY KEY, uname VARCHAR(20) NOT NULL, uemail VARCHAR(20) NOT NULL, ucity VARCHAR(20), upassw VARCHAR(20) NOT NULL ); CREATE TABLE songs( sid INT AUTO_INCREMENT PRIMARY KEY, sname VARCHAR(20) NOT NULL, srldate DATE NOT NULL ); CREATE TABLE albums ( albid INT AUTO_INCREMENT PRIMARY KEY, albname VARCHAR(20) NOT NULL, albrldate DATE NOT NULL, albrltime TIME NOT NULL ); CREATE TABLE artists ( aid INT AUTO_INCREMENT PRIMARY KEY, aname VARCHAR(20) NOT NULL ); CREATE TABLE

2021-09-25 03:04:41    分类:技术分享    mysql   sql   foreign-keys   constraints   mysql-error-1064

MySQL error: Cannot add foreign key constraint?

There always be the error:"Cannot add foreign key constraint" when I create my last table. System: Mac OS X 10.9 DB : MySQL 5.6.14 DBM : Sequel Pro CREATE TABLE users ( uid INT AUTO_INCREMENT PRIMARY KEY, uname VARCHAR(20) NOT NULL, uemail VARCHAR(20) NOT NULL, ucity VARCHAR(20), upassw VARCHAR(20) NOT NULL ); CREATE TABLE songs( sid INT AUTO_INCREMENT PRIMARY KEY, sname VARCHAR(20) NOT NULL, srldate DATE NOT NULL ); CREATE TABLE albums ( albid INT AUTO_INCREMENT PRIMARY KEY, albname VARCHAR(20) NOT NULL, albrldate DATE NOT NULL, albrltime TIME NOT NULL ); CREATE TABLE artists ( aid INT AUTO

2021-09-24 16:16:24    分类:问答    mysql   sql   foreign-keys   constraints   mysql-error-1064

Python PuLP Beginner Constraint lists

I am a beginner in Python. I am using PuLP to solve a minimization problem for a Renewable Energy System (PV + Wind + Battery). My system uses timesteps (24h, per hour). My question is how can I create a list in the constraints that collects the state of charge of the battery, as well as the inlet and outlet of it (variables that change value each timestep). In mathlab I have seen people use "eye", but here in PuLP I am not sure how can be done. Any help would be very well appreciated. Here is part of the code I have (which I know, is not correct). import numpy as np import pandas as pd from

2021-09-24 05:24:36    分类:问答    python   python-3.x   list   constraints   pulp

How do I change the font size according to screen size

I have added min font size to label but the font is not changing according to the screen size. I thought setting min font size and using autolayout is to scale the label height is enough. But its not happening.

2021-09-24 04:56:24    分类:问答    ios   fonts   autolayout   uilabel   constraints

视图加载后 iOS 自动布局约束的跳转(iOS Auto Layout Constraint's Jumping After View Has Loaded)

问题 在这里制作了一个快速视频来演示这个问题:https://vid.me/9kB5 当我删除约束时,文本不会在加载视图时跳转。 但随后它就违背了目的。 当我设置约束时,我使用了“重置为建议的约束” 有任何想法吗? 回答1 这不是约束问题。 您的视图位于导航栏下方。 您可以通过取消选中页面视图控制器场景中的“扩展边缘 - 顶栏下方”来修复故事板。 在代码中 - (void)viewDidLoad { [super viewDidLoad]; self.edgesForExtendedLayout = UIRectEdgeNone; } 回答2 不过,Hari Kunwar 的回答对我不起作用。 有效的是改变我视图的顶部约束(那个跳跃的......也是顶部的那个)。 我的顶部约束是顶部布局指南 - 我删除了它,现在当我添加时,我选择了约束常量附近的小箭头,并选择了视图而不是顶部布局指南......

2021-09-23 16:34:08    分类:技术分享    ios   autolayout   constraints

在 Tab Swift 中使用页面视图控制器(Using Page View Controller inside Tab Swift)

问题 我目前的工作: 所以我有一个看起来像这样的标签栏: 当我点击“Canteen”时,我想被定向到一个页面视图控制器,在那里我可以在不同的页面之间滑动但保持在同一个选项卡上。 我有这个有点工作: 我有这样的故事板设置: 如您所见,上面的 segue 来自 Tab Bar Controller。 第三个视图(Can Page Item Controller,ID:“CanItemController)用于页面视图中的所有页面。 上面的第二个视图(页面视图控制器,ID:“CanPageController)用于控制页面(废话) 第一个视图 (CanteenViewController) 包含所有代码并建立所有连接。 这就是一切继续的地方。 这个类里面的代码在这里: import UIKit class CanteenViewController: UIViewController, UIPageViewControllerDataSource { // MARK: - Variables private var pageViewController: UIPageViewController? private let contentImages = ["Radar-512.png", "dartp.png", "roomp.png", "abnews.png", "canteenp

2021-09-23 15:59:50    分类:技术分享    ios   swift   uitabbarcontroller   constraints   uipageviewcontroller

Oracle Unique Constraint - Trigger to check value of property in new relation

Hi I'm having trouble getting my sql syntax correct. I want to create a unique constraint that looks at the newly added foreign key, looks at some properties of the newly related entity to decided if the relationship is allowed. CREATE or replace TRIGGER "New_Trigger" AFTER INSERT OR UPDATE ON "Table_1" FOR EACH ROW BEGIN Select "Table_2"."number" (CASE "Table_2"."number" > 0 THEN RAISE_APPLICATION_ERROR(-20000, 'this is not allowed'); END) from "Table_1" WHERE "Table_2"."ID" = :new.FK_Table_2_ID END; Edit: APC answer is wonderfully comprehensive, however leads me to think im doing it in the

2021-09-23 11:17:02    分类:问答    sql   database   oracle   triggers   constraints

Neo4J 约束中的非空属性(Not null attribute in Neo4J constraint)

问题 是否可以在 Neo4J 数据库中为属性不为空创建约束? 就像是: CREATE CONSTRAINT ON (p:Person) ASSERT p.name IS NOT NULL 回答1 它已为 Neo4j 2.3 计划并已实现,应可用于 2.3.RC1

2021-09-22 08:10:15    分类:技术分享    neo4j   constraints   cypher

使用 R nloptr 包进行最小化 - 多重等式约束(Minimization with R nloptr package - multiple equality constraints)

问题 是否可以在 R 中的nloptr函数中指定多个等式约束? 我试图运行的代码如下: eval_f <- function( x ) { return( list( "objective" = x[3]^2+x[4]^2, "gradient" = c( 0, 0, 2*x[3], 2*x[4] ) ) ) } # constraint functions # equalities eval_g_eq <- function( x ) { constr <- c( x[1] + x[2] + x[3] - 4, x[1]^2 + x[2]^2 + x[4] - 15 ) grad <- c( c(1, 1, 1, 0), c(2*x[1], 2*x[2], 0, 1) ) return( list( "constraints"=constr, "jacobian"=grad ) ) } # initial values x0 <- c( 1, 5, 5, 1 ) local_opts <- list( "algorithm" = "NLOPT_LD_MMA", "xtol_rel" = 1.0e-7 ) opts <- list( "algorithm" = "NLOPT_LD_AUGLAG", "xtol_rel" = 1.0e-7, "maxeval" = 1000,

2021-09-22 07:52:18    分类:技术分享    r   constraints   equality   nonlinear-optimization   nlopt