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Can a foreign key be NULL and/or duplicate?
...mply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition. Null by definition is not a value. Null means that we do not yet know what the value is.
Let me give you a real life example. Suppose you have a database that sto...
【解决】Linux mysql如何重置root密码？ - 更多技术 - 清泛网 - 专注C/C++及内核技术
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4. 略过grant授权表启动mysql/MariaDB服务
启用--skip-grant-tables选项后，任何人都可以在没有密码和所有权限的情况下连接到数据库服务器：
mysqld_safe --skip-grant-tables &
上面命令末尾的＆符号将导致程序在后台运行，因此我...
mysqldump data only
...for the syntax for dumping all data in my mysql database. I don't want any table information.
8 Answers
...
Remove all spaces from a string in SQL Server
... trim() or worry about multiple spaces for either char or varchar:
create table #t (
c char(8),
v varchar(8))
insert #t (c, v) values
('a a' , 'a a' ),
('a a ' , 'a a ' ),
(' a a' , ' a a' ),
(' a a ', ' a a ')
select
'"' + c + '"' [IN], '"' + replac...
Saving changes after table edit in SQL Server Management Studio
If I want to save any changes in a table, previously saved in SQL Server Management Studio (no data in table present) I get an error message:
...
Is there an SQLite equivalent to MySQL's DESCRIBE [table]?
...ed learning SQLite . It would be nice to be able to see the details for a table, like MySQL's DESCRIBE [table] . PRAGMA table_info [table] isn't good enough, as it only has basic information (for example, it doesn't show if a column is a field of some sort or not). Does SQLite have a way to do t...
Is there a better way to dynamically build an SQL WHERE clause than by using 1=1 at its beginning?
... offer you:
using (var dbContext = new MyDbContext())
{
IQueryable<Table1Item> query = dbContext.Table1;
if (condition1)
{
query = query.Where(c => c.Col1 == 0);
}
if (condition2)
{
query = query.Where(c => c.Col2 == 1);
}
if (condition3)...
How to print the contents of RDD?
...
c.take(10)
and Spark newer version will show table nicely.
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How to make a div fill a remaining horizontal space?
...om the display property.
Basically you need to make the two divs act like table cells. So instead of using float:left, you'll have to use display:table-cell on both divs, and for the dynamic width div you need to set width:auto; also. The both divs should be placed into a 100% width container with ...
What is the performance cost of having a virtual method in a C++ class?
...ss (or any of its parent classes) means that the class will have a virtual table, and every instance will have a virtual pointer.
...