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Best practices for SQL varchar column length [closed]
... table's varchar column. But I could not find any reference for that.
For MySQL the manual says "In most cases, ALTER TABLE makes a temporary copy of the original table". And my own tests confirm that: running an ALTER TABLE on a table with 1.2 million rows (the same as in my test with Postgres) to...
ZMQ: 基本原理 - 开源 & Github - 清泛网移动版 - 专注C/C++及内核技术
...。
本文的目的是解释ØMQ架构的基本概念，它们是如何组合起来的，以及它们被如此设计的原因。
拓扑
拓扑是ØMQ最主要的概念，除非你知道“拓扑”代表什么，否则将与其他概念混淆更难...
LIMIT 10..20 in SQL Server
... not part of standard SQL. It's supported as a vendor extension to SQL by MySQL, PostgreSQL, and SQLite.
Other brands of database may have similar features (e.g. TOP in Microsoft SQL Server), but these don't always work identically.
It's hard to use TOP in Microsoft SQL Server to mimic the LIMI...
count(*) vs count(column-name) - which is more correct? [duplicate]
...
there is a performance difference (at least in MySQL) as well (see my answer).
– nickf
Jun 9 '10 at 7:51
1
...
常用Sql - 数据库(内核) - 清泛网 - 专注C/C++及内核技术
常用Sqlmysql：drop table if exists tablename;不能写成drop table tablename if exists tablename;mysql：建立索引SqlCREATE TABLE t...mysql：drop table if exists tablename;
不能写成
drop table tablename if exists tablename;
mysql：建立索引Sql
CREATE TABLE tablename (
`ID...
PHP的函数前加上“@”的作用 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...供的错误信息屏蔽的专用符号。比如在一个函数前使用@@mysql_query 不会出现Warning，而原来mysql_query 在遇到错误时会在页面上访提示Warning。@是PHP提供的错误信息屏蔽的专用符号。
比如在一个函数前使用@
@mysql_query 不会出现Warning...
Curses library not found. Please install appropriate package - 更多...
Curses library not found. Please install appropriate packageCentOS安装MySql报错：-- Could NOT find Curses (missing: CURSES_LIBRARY CURSES_INCLUDE_PATH)CMake Error at cmake readli...CentOS安装MySql报错：
-- Could NOT find Curses (missing: CURSES_LIBRARY CURSES_INCLUDE_PATH)
CMake Err...
UTF-8: General? Bin? Unicode?
...only one-to-one comparisons between characters.
Quoted from:
http://dev.mysql.com/doc/refman/5.0/en/charset-unicode-sets.html
For more detailed explanation, please read the following post from MySQL forums:
http://forums.mysql.com/read.php?103,187048,188748
As for utf8_bin:
Both utf8_general_ci...
Count the number of occurrences of a string in a VARCHAR field?
...test 0
test4 valuevaluevaluevaluevalue 5
I don't have MySQL install, but goggled to find the Equivalent of LEN is LENGTH while REPLACE is same.
So the equivalent query in MySql should be
SELECT TITLE,DESCRIPTION, (LENGTH(DESCRIPTION) - LENGTH(REPLACE(DESCRIPTION, 'value', ''))...
In MySQL queries, why use join instead of where?
... Performance Perspective:
Where supported (Oracle 9i+, PostgreSQL 7.2+, MySQL 3.23+, SQL Server 2000+), there is no performance benefit to using either syntax over the other. The optimizer sees them as the same query. But more complex queries can benefit from using ANSI-92 syntax:
Ability to ...