constraints

问题 Is there any way to add constraints or foreign keys the way I would in a database? E.g. making sure a field is unique, a field is always > 0, that customer_id in the orders table always has a match in customer_id in the customer table, etc? 来源： https://stackoverflow.com/questions/32353732/python-pandas-can-i-add-constraints-like-i-would-in-a-database

问题 Does anybody know how to write conditional constraint in mixed integer programming for this case: if a == 0 then b = 1 else b = 0 -M <= a <= M b={0,1} Note that M can be any continuous number. Thanks. Regards, 回答1: I would approach this as follows. First use a variable splitting approach by introducing two non-negative variables aplus, amin : 0 <= aplus <= d*M 0 <= amin <= (1-d)*M a = aplus-amin d in {0,1} Now we can do: 0.001*(1-b) <= aplus + amin <= M*(1-b) In many cases we can simplify

问题 it's my first post here and I'm posting for my team of learning Java programmer for an school project. So we aren't good programmer. how can I add a constraint to make the Optaplanner move the lectures into a specific room type. For example I want to move the lecture "Programming" into a computerroom and the lecture "Math" in a normal room. But with my constraint it declares the hard constraints but doesn't move the lectures in their room. This should be a negative constraint. So the negative

问题 I have an image whose width = 189, height = 41, so I defined 2 constraints for this UIImageView like this: NSArray *constraint_V=[NSLayoutConstraint constraintsWithVisualFormat:@"V:[Title(41)]" options:0 metrics:nil views:viewsDictionary]; [imgVwLogo addConstraints:constraint_V]; NSArray *constraint_H=[NSLayoutConstraint constraintsWithVisualFormat:@"H:[Title(189)]" options:0 metrics:nil views:viewsDictionary]; [imgVwLogo addConstraints:constraint_H]; It looks good on iPhone 4s, but when it

问题 I'd like to limit the entries in a table. Let's say in table tBoss . Is there a SQL constraint that checks how many tuples are currently in the table? Like SELECT COUNT(*) from tBoss < 2 Firebird says: Invalid token. Dynamic SQL Error. SQL error code = -104. Token unknown - line 3, column 8. SELECT. Thanks. Norbert 回答1: Does your database have triggers? If so, Add a trigger that rolls back any insert that would add more than 2 rows... Create Trigger MyTrigName For Insert On tBoss As If

问题 I've a UIImageView that holds a profile image in my app. The aspect is "Aspect Fit". But I have some problems. I've pinned a contraint from the UIImageView to the larger UImageView above and with the leading space to superView. but it looks like this on runtime: Way too big and placed wrongly. It also looks like this in IB: What should I be doing to achieve the right behaviour here? Thanks! Erik 回答1: You image view is resizing itself based on the image you set it to display. This behaviour

问题 I need to identify the row that caused a constraint check to fail after an INSERT OR IGNORE statement. I need this for a tool that generates SQL statements, so I can't tie this to a specific use case with a particular table. The challenge here is that I can't know which constraints are set for the particular table that I will insert into. It may have foreign key or UNIQUE constraints, or even a CHECK clause attached. So, all I can learn from the INSERT is that it has failed. Now, how to I

问题 I am trying to set constraints to perform optimization with the help of mystic package. I executed the code in Spyder and PyCharm IDE. In both cases kernel crashed. When I have only 2 line string 'simplify'-method works fine. Trying to set greater than 2 lines constraints leads to kernel's death. import mystic.symbolic as ms equation = """ x0*7.2 + x1*1.9 + x2*35.7 + x3*4.1 + x4*23.0 + x5*19.2 + x6*0.0 + x7*0.0 + x8*0.0 + x9*0.0 + x10*10.1 + x11*10.8 + x12*11.3 + x13*14.8 + x14*78.6 + x15*5.8

问题 original table is more complicated but.. i got a table which stores great many trees inside like; what im looking is a nontrigger mothod like constraint or a trigger which decides to rollback very fast.. create table myTreeTable ( id int not null identity(1,1), node varchar(80), parent varchar(80), constraint PK_mytable primary key nonclustered (node) ) insert into myTreeTable values ('a', null) insert into myTreeTable values ('b', 'a') insert into myTreeTable values ('c', 'a') insert into

问题 let's say I have a large table. This table not need to be queried, I just want to save the data inside for a while. I want to prevent duplicates rows in the table, so I want to add an unique constraint (or PK) on the table. But the auto-created unique index is realy unnecessary. I don't need it, and it's just wasting space in disk and require a maintenance (regardless of the long time to create it). Is there a way to create an unique constraint without index (any index - unique or nonunique)?