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How can I rename a database column in a Ruby on Rails migration?
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rename_column :table, :old_column, :new_column
You'll probably want to create a separate migration to do this. (Rename FixColumnName as you will.):
script/generate migration FixColumnName
# creates db/migrate/xxxxxxxxxx_fix_column_name....
SQL/mysql - Select distinct/UNIQUE but return all columns?
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You're looking for a group by:
select *
from table
group by field1
Which can occasionally be written with a distinct on statement:
select distinct on field1 *
from table
On most platforms, however, neither of the above will work because the behavior on the other co...
Can someone explain mappedBy in JPA and Hibernate?
...irline that it is responsible for maintaining the values over in the other table. It is possible to tell an Entity it "owns" a column in a different table and is responsible for updating it. It's not something you usually want to do and can cause problems with the order SQL statements are executed...
LINQ to SQL Left Outer Join
..."left" row in a left-outer-join will match 0-n "right" rows (in the second table), where-as yours matches only 0-1. To do a left outer join, you need SelectMany and DefaultIfEmpty, for example:
var query = from c in db.Customers
join o in db.Orders
on c.CustomerID equals o...
Difference Between Schema / Database in MySQL
...racle Database product, a schema represents only a part of a database: the tables and other objects owned by a single user.
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What's the purpose of SQL keyword “AS”?
You can set table aliases in SQL typing the identifier right after the table name.
9 Answers
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Do I need to create indexes on foreign keys on Oracle?
I have a table A and a table B . A has a foreign key to B on B 's primary key, B_ID .
7 Answers
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App Inventor 2 SQLite 拓展：超流行兼容主流SQL语法的迷你本地数据库引擎...
...数据表
创建一个测试数据表，sql如下：
CREATE TABLE users (
id INTEGER PRIMARY KEY,
name TEXT,
age INTEGER);
数据表信息
这时，可以查看一下表信息：
插入数据
往 users 表中插入...
Lua简明教程 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...foo(x) return x^2 end
foo = function(x) return x^2 end
Table
所谓Table其实就是一个Key Value的数据结构，它很像Javascript中的Object，或是PHP中的数组，在别的语言里叫Dict或Map，Table长成这个样子：
1
haoel = {name=...
Transaction isolation levels relation with locks on table
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I want to understand the lock each transaction isolation takes on the table
For example, you have 3 concurrent processes A, B and C. A starts a transaction, writes data and commit/rollback (depending on results). B just executes a SELECT statement to read data. C reads and updates data. All t...