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Assign multiple columns using := in data.table, by group
What is the best way to assign to multiple columns using data.table ? For example:
2 Answers
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Oracle find a constraint
...stem generated constraint name. For instance, if we specify NOT NULL in a table declaration. Or indeed a primary or unique key. For example:
SQL> create table t23 (id number not null primary key)
2 /
Table created.
SQL> select constraint_name, constraint_type
2 from user_constraint...
PostgreSQL - max number of parameters in “IN” clause?
... possible if the inputs are all scalars (no RowExprs) and there is a
* suitable array type available. If not, we fall back to a boolean
* condition tree with multiple copies of the lefthand expression.
* Also, any IN-list items that contain Vars are handled as separate
* boolean conditions, bec...
Why does C++11 not support designated initializer lists as C99? [closed]
...me it has failed
Ben Voigt's comments have helped me to see the insurmountable problems with this approach; given:
struct X {
int c;
char a;
float b;
};
What order would these functions be called in in c99: struct X foo = {.a = (char)f(), .b = g(), .c = h()}? Surprisingly, in c99:
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Make column not nullable in a Laravel migration
I'm writing a migration to make certain columns in a table nullable right now. For the down function, I of course want to make those columns not nullable again. I looked through the schema builder docs , but couldn't see a way to do this.
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What is the difference between a schema and a table and a database?
...bably a n00blike (or worse) question. But I've always viewed a schema as a table definition in a database. This is wrong or not entirely correct. I don't remember much from my database courses.
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How to convert boost path type to string?
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@MarcoAlka See the linked table boost.org/doc/libs/1_48_0/libs/filesystem/v3/doc/… and note the second line: class path canonize() Function removed - that means it was once in the library but no longer--the definition of deprecated.
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How does std::forward work? [duplicate]
...thing using another mysterious thing. This particular cast is defined by a table in Xeo's answer. But the question is: Why? So here's my understanding:
Suppose I want to pass you an std::vector<T> v that you're supposed to store in your data structure as data member _v. The naive (and safe) s...
How can I make a JPA OneToOne relation lazy
... a proxy object or NULL and it can't determine that by looking at its base table's columns due to one-to-one normally being mapped via shared PK, so it has to be eagerly fetched anyway making proxy pointless. Here's a more detailed explanation.
many-to-one associations (and one-to-many, obviously) d...
What is the optimal length for user password salt? [closed]
...ices for how long the salt should be? I'll be storing the salt in my user table, so I would like the best tradeoff between storage size and security. Is a random 10 character salt enough? Or do I need something longer?
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