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Importance of varchar length in MySQL table
I have a MySQL table where rows are inserted dynamically. Because I can not be certain of the length of strings and do not want them cut off, I make them varchar(200) which is generally much bigger than I need. Is there a big performance hit in giving a varchar field much more length than necessar...
Mysql ibdata 丢失或损坏如何通过frm&ibd 恢复数据 - 爬虫/数据库 - 清...
...这个方法不能恢复你的数据。my.ini的设置为 innodb_file_per_table = 1。参考 http://blog.chinaunix.net/uid-24111901-id-2627876.html1、找回表结构，如果表结构没有丢失直接到下一步
a、先创建一个数据库，这个数据库必须是没有表和任何操作的...
How to scroll to the bottom of a UITableView on the iPhone before the view appears
I have a UITableView that is populated with cells of a variable height. I would like the table to scroll to the bottom when the view is pushed into view.
...
Rails 3: Get Random Record
...ils 3 all examples will work. But using order RANDOM is quite slow for big tables but more sql-style
UPD. You can use the following trick on an indexed column (PostgreSQL syntax):
select *
from my_table
where id >= trunc(
random() * (select max(id) from my_table) + 1
)
order by id
limit 1...
Mysql ibdata 丢失或损坏如何通过frm&ibd 恢复数据 - 更多技术 - 清泛网 - ...
...这个方法不能恢复你的数据。my.ini的设置为 innodb_file_per_table = 1。
参考 http://blog.chinaunix.net/uid-24111901-id-2627876.html
1、找回表结构，如果表结构没有丢失直接到下一步
a、先创建一个数据库，这个数据库必须是没有表和任何操...
How to use index in select statement?
Lets say in the employee table, I have created an index(idx_name) on the emp_name column of the table.
8 Answers
...
JOIN queries vs multiple queries
...
if you are joining 3 or more tables on different keys, often databases (i.e. mysql) can only use one index per table, meaning maybe one of the joins will be fast (and use an index) whereas the others will be extremely slow. For multiple queries, you can ...
How to reorder data.table columns (without copying)
I'd like to reorder columns in my data.table x , given a character vector of column names, neworder :
2 Answers
...
PostgreSQL function for last inserted ID
In PostgreSQL, how do I get the last id inserted into a table?
10 Answers
10
...
conditional unique constraint
...unt > 0.
http://msdn.microsoft.com/en-us/library/ms188258.aspx
CREATE TABLE CheckConstraint
(
Id TINYINT,
Name VARCHAR(50),
RecordStatus TINYINT
)
GO
CREATE FUNCTION CheckActiveCount(
@Id INT
) RETURNS INT AS BEGIN
DECLARE @ret INT;
SELECT @ret = COUNT(*) FROM CheckConstraint WHER...