constraints | 易学教程

iOS - Placing two label together in centre of their super view

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问题 I have two label, L1 and L2 of variable and nonidentical length. I want to place these two label using constraints in Xcode. If possible i don't want to manipulate constraints programmatically. guidance will be appreciated. Right image should be the expected output Requirements, Two labels are non identical in width When running leading space of L1 and trailing space of L2 will be equal distance between L1 & L2, horizontal space is fixed, 10 px UIStackView cannot be used How can I do it from

Why most SQL databases allow defining the same index twice?

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问题 Why most SQL databases allow defining the same index (or constraint) twice? For example in MySQL I can do: CREATE TABLE testkey(id VARCHAR(10) NOT NULL, PRIMARY KEY(id)); ALTER TABLE testkey ADD KEY (id); ALTER TABLE testkey ADD KEY (id); SHOW CREATE TABLE testkey; CREATE TABLE `testkey` ( `id` varchar(10) NOT NULL, PRIMARY KEY (`id`), KEY `id` (`id`), KEY `id_2` (`id`) ) I do not see any use case for having the same index or constraint twice. And I would like SQL databases not allowing me do

MySQL InnoDB constraint does not work

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I stumble upon strange behavior with innoDB constraint, and cannot find cause of it. I have tables with data. Below listed their structures: CREATE TABLE `contents` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `title` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`), KEY `title` (`title`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE `fields` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(45) NOT NULL, `type` varchar(45) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `nameUNIQUE` (`name`), KEY `name` (`name`), KEY `type` (`type`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE

Constrain the number of child entities in Entity Framework

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Bottom Line Up Front Is there a succinct way that I can constrain the number of child entities that can belong to a parent in Entity Framework. I am using 4.3.1 at the moment. The Problem I am developing an ASP.NET MVC3 site which accesses data via a data access layer that uses Entity Framework. I have a SearchList entity which has a many to many relationship to a Search entity. A SearchList may have many Searches, and a Search may belong to many SearchLists. At one point in the workflow of the site, a user needs to select the searches and other items to use in a batch search. We want the page

Regression with equality and inequality constrained coefficients in R

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I am trying to obtain estimated constrained coefficients using RSS. The beta coefficients are constrained between [0,1] and sum to 1. Additionally, my third parameter is constrained between (-1,1). Utilizing the below I can obtain a nice solution using simulated variables but when implementing the methodology on my real data set I keep arriving at a non-unique solution. In turn, I'm wondering if there is a more numerically stable way to obtain my estimated parameters. set.seed(234) k = 2 a = diff(c(0, sort(runif(k-1)), 1)) n = 1e4 x = matrix(rnorm(k*n), nc = k) a2 = -0.5 y = a2 * (x %*% a) +

Cross table constraints in PostgreSQL

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问题 Using PostgreSQL 9.2.4, I have a table users with a 1:many relation to the table user_roles . The users table stores both employees and other kinds of users. Table "public.users" Column | Type | Modifiers -----------------+-------------------+----------------------------------------------------- uid | integer | not null default nextval('users_uid_seq'::regclass) employee_number | character varying | name | character varying | Indexes: "users_pkey" PRIMARY KEY, btree (uid) Referenced by: TABLE

Oracle trigger that check constraint on a monthly basis

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just wonder is it possible to create a trigger to check on a specify constraint base on monthly basis. eg. table rent |ID|Member|book| ---------------------- 1 | John |fairytale| 2 | John |friction| 3 | John |comic| 4 | John |magazine| constraint : member are only allow to borrow 4 books monthly. i thought of using count(book) <= 4 but does not know how to implement the monthly basis constraint. Any suggestion? using a trigger, whilst it seems to work, is a dangerous way of doing it, as sessions running in parallel wont see the inserted data from the inprogress session. you can do it via a

Referring MySQL ENUM in another table

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I have a table SkillLevel created as CREATE TABLE `sklllevel` ( `Name` varchar(20) NOT NULL, `level` enum('No Experience','Beginner','Expert','Advisor') DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8; With Values INSERT INTO test.sklllevel (name,level) values ('No Experience','No Experience'),('Beginner','Beginner'),('Expert','Expert'),('Advisor','Advisor'); I want to refer SkillLevel.Level with testSkill.tkSkill in another table created as: CREATE TABLE `testskill` ( `pkid` int(11) NOT NULL, `name` varchar(45) DEFAULT NULL, `tkSkill` tinyint(4) DEFAULT NULL, PRIMARY KEY (`pkid`) ) ENGINE

Trigger to silently ignore/delete duplicate entries on INSERT

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问题 I have the following table: T(ID primary key, A, B) I want to have pair (A, B) unique but I don't want to have constraint unique(A,B) on them because it will give error on insert. Instead I want MySQL to silently ignore such inserts. I can't use "insert on duplicate keys ignore" because I can't control client's queries. So, can I build such trigger? Or maybe there is some constraint that allows silent ignore? Edit: I dug around and I think I want something like SQLite's "Raise Ignore"

Unity Final VR IK (Asset) lock person in sitting position

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Currently I am working on a game for people with accessibility restrictions. I am having the issue of locking the player model in a sitting position. If the user does not center themselves in the room the player model will be pulled to a certain direction. I would like to lock the player model in a seat and only allow for arm movements and head rotations, no leaning or moving in the game using the HMD. Since I am using the Final VR IK asset I have tried using their demo for sitting position in VR and cannot get the player to stay seated naturally. I am not sure how to program this or set