大约有 6,100 项符合查询结果（耗时：0.0170秒） [XML]
sqlalchemy unique across multiple columns
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UniqueConstraint or Index constructs explicitly.
As these belong to a Table and not to a mapped Class, one declares those in the table definition, or if using declarative as in the __table_args__:
# version1: table definition
mytable = Table('mytable', meta,
# ...
Column('customer_id',...
Is there a version control system for database structure changes?
...the version (such as removing a column). Each migration is numbered, and a table keeps track of your current db version.
To migrate up, you run a command called "db:migrate" which looks at your version and applies the needed scripts. You can migrate down in a similar way.
The migration scripts the...
Entity Framework vs LINQ to SQL
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LINQ to SQL only supports 1 to 1 mapping of database tables, views, sprocs and functions available in Microsoft SQL Server. It's a great API to use for quick data access construction to relatively well designed SQL Server databases. LINQ2SQL was first released with C# 3.0 and...
How many concurrent AJAX (XmlHttpRequest) requests are allowed in popular browsers?
...cript">
var _settimer;
var _timer;
var _waiting;
$(function(){
clearTable();
$('#boton').bind('click', donow);
})
function donow(){
var w;
var estim = 0;
_waiting = $('#total')[0].value * 1;
clearTable();
for(var r=1;r<=_waiting;r++){
w = Math.floor(Math.random()*6)+2;
...
What is NSLayoutConstraint “UIView-Encapsulated-Layout-Height” and how should I go about forcing it
I have a UITableView running under iOS 8 and I'm using automatic cell heights from constraints in a storyboard.
17 Answer...
jQuery - Get Width of Element when Not Visible (Display: None)
... visible width() returns 0. Makes sense, but I need to get the width of a table in order to set the width of the parent before I show the parent.
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How to know when UITableView did scroll to bottom in iPhone
I would like to know when a UITableView did scroll to bottom in order to load and show more content, something like a delegate or something else to let the controller know when the table did scroll to bottom.
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SQL join on multiple columns in same tables
... subqueries, but I'm having trouble joining columns together from the same tables. I tried:
2 Answers
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Auto Generate Database Diagram MySQL [closed]
... every project. Is there a tool out there that will let me select specific tables and then create a database diagram for me based on a MySQL database? Preferably it would allow me to edit the diagram afterward since none of the foreign keys are set...
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Count number of rows within each group
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An old question without a data.table solution. So here goes...
Using .N
library(data.table)
DT <- data.table(df)
DT[, .N, by = list(year, month)]
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