records

MySQL Internals-Index Merge优化 Louis Hust 0 前言 之前搞错了，以为Index Merge是MySQL5.6的新特性，原来不是，发现5.5也有，看了下manual，发现5.0的manual就已经存在了， 可以说是一个历史悠久的优化手段了，好吧，不管怎么样，今天就拨开其神秘的面纱，看看其内部到底如何生成这种Index Merge的计划的。 这里只详细介绍Intersect操作，对于Union和Sort-Union的具体代码，还没开始研究。 1 Index Merge理论基础 Index Merge——索引归并，即针对一张表，同时使用多个索引进行查询，然后将各个索引查出来的结果进行进一步的操作，可以是求交 ——Intersect，也可以是求和——Union，针对union还有一种补充算法——Sort-Union，很奇怪为什么没有Sort-Intersect，按道理也是可以做的。 什么情况下，同时使用多个索引会有利呢？比如说WHERE条件是C1=10 AND C2 =100，但是只有分别针对C1和C2的索引，而没有(C1,C2)这种索引， 两个索引同时使用才有意义,通过两个索引都可以快速定位到一批数据，然后对这一批数据进行进一步的求交或求和操作即可,这样的效率可能比 全表扫描或者只使用其中一个索引进行扫描然后再去主索引查询要快。

创建 config.ini `#需要合并的服务器 最大2 db_app_count = 1 需要合并资源1 db_host1 = 127.0.0.1 db_user1 = root db_pass1 = root 需要合并资源2 db_host2 = 127.0.0.1 db_user2 = root db_pass2 = root 目的地 db_host = 127.0.0.1 db_user = root db_pass = root #需要合并的表 db_list = [] #新服serverId server_id = 8 新服数据库目的地 db_host1 = 127.0.0.1 db_user1 = root db_pass1 =root #用户登录数据login db_host2 = 127.0.0.1 db_user2 = root db_pass2 = root 资源 db_host = 127.0.0.1 db_user = root db_pass = root #需要导入资源 db_list = [] ` 没怎么写过,网上查了下语法,可能不规范,大致就是这个样子的 linux一般默认版本为2. 需要更新python版本到3. 需要安装pip3 命令 需要 pip3安装records pymysql 两个库 数据库信息,表信息,通过配置文件config配置完成

What is difference between tuples and records? Both are product types which let you build types from multiple simpler types. Some languages treat tuples as a kind of record. Definitions A tuple is an ordered group of elements, like (10, 25). A record is typically a group of named elements like { "x": 10, "y": 25 } where the value has two fields labelled x and y and the value of field x is 10 . Etymology The word "tuple" comes from the common "-tuple" suffix on "quintuple", "sextuple", "septuple", "octuple" which mean groups of 5, 6, 7, and 8 respectively. The word "record" comes from data

This question already has an answer here: How to delete multiple rows in SQL where id = (x to y) 5 answers This is probably a very simple question for somebody with experience, but I just wanted to know the safest way to delete a couple of hundred records in an SQL table that fall between a specific range. For example I need to delete rows with an ID between 79 & 296: My worry is if I say delete everything with an ID (>79 AND < 296) then it may literally wipe the whole table. if you use Sql Server delete from Table where id between 79 and 296 After your edit : you now clarified that you want :

Replacing fields names with letters, I have cases like this: data Foo = Foo { a :: Maybe ... , b :: [...] , c :: Maybe ... , ... for a lot more fields ... } deriving (Show, Eq, Ord) instance Writer Foo where write x = maybeWrite a ++ listWrite b ++ maybeWrite c ++ ... for a lot more fields ... parser = permute (Foo <$?> (Nothing, Just `liftM` aParser) <|?> ([], bParser) <|?> (Nothing, Just `liftM` cParser) ... for a lot more fields ... -- this is particularly hideous foldl1 merge [foo1, foo2, ...] merge (Foo a b c ...seriously a lot more...) (Foo a' b' c' ...) = Foo (max a a') (b ++ b') (max c