teradata index

Label:Sometimes you need to index a long character column, which makes the index larger and slower. One strategy is to emulate a hash index. But sometimes it's not good enough, then?You can usually index the beginning of several characters, rather than all values, to save space and get good performance. This makes the

Main Memory index node and secondary index node are mainly reflected in: Memory index node State; Device number, index node number; reference count.Main Memory Index node state-reflects the use of main memory index nodes. It indic

Tags: style using SP data on BS time new asA structure that sorts the values of one or more columns in a database table, using an index to quickly access specific information in a database tableAdvantages:First, by creating a unique index, you can guarantee the uniqueness of each row of data in a database table. Second, it can greatly speed up the retrieval of data, which is the main reason for creating ind

Create a table first Create table 'menu _ employee '( 'Id' int (11) not null AUTO_INCREMENT COMMENT 'auto-incrementing primary key, no practical significance ', 'Employee _ pid 'int (5) default null comment' parent node serial number, which is generally the Department serial number, but there are exceptions and no group employees ', 'Employee _ id' int (5) default null comment' employee number, Department number + employee number ', 'Employee _ name' varchar (100) DEFAULT ''' COMMENT 'employee n

Further discussion on who is in front of the two index columns in the composite index -- Practice, index -- Further discussion on who is in front of the two index columns in the composite index -- Practice: The last time I talked about this example in the elder's QQ group: c

[Oracle]-[Index]: check data before creating an index, or create an index before inserting data. Problem: 1. Create a new table structure and create an index, import millions or tens of millions of data into the table using insert. 2. Create a new table structure, use isnert to import millions or tens of millions of da

TTL index:The TTL collection enables MongoDB to set the expiration time for stored data, after a specified period of time, or at a specified point in time, the collection is automatically cleared by Mongod. This feature facilitates the storage of some data that only needs to be kept for a certain amount of time, such as event data generated by the machine, logs, session information, and so on.First create a collection ttlcol:The TTL index is created a

Http://www.cnblogs.com/osfipin/p/4943229.html-Article addressBtree retrieval speed without hash fast.But now the hash is used very little, reason:1:hash can only be queried with =, in, 2:hash cannot be combined with other indexes at the same time.3:hash Index of the field, if the value of a large number of duplicates, will lead to query efficiency and so on.4:hash are unordered, with neither physical nor logical ordering.Feedback-mysql

Heaps (heap)This structure is called a heap because it is not arranged in a logical order that is specified by anyone. Instead, they are organized according to partitioned data. In other words, the physical order of the disks is followed. As long as the data file that needs to be read does not have file system fragmentation (note the fragmentation of the index mentioned below), the read process can be carried out continuously on disk without the extra

Label:An index is an on-disk structure associated with a table or view, which speeds up the retrieval of rows from a table or view. An index contains keys that are generated by one or more columns in a table or view. These keys are stored in a structure (B-tree), allowing SQL Server to quickly and efficiently find the rows associated with the key value. A table or view can contain the following types of ind

1. What is an aggregated index (clustered index)/What is a non-aggregated index (nonclustered)?The index can be understood as a special kind of directory. Microsoft's SQL Server provides two types of indexes: Clustered indexes (clustered index, also called clustered indexes,

Label:Index type 1. Unique index: Unique index does not allow two rows to have the same index value 2. Primary KEY index: Defining a primary key for a table will automatically create a primary key index, which is a special type of unique

From: http://crm.xingfa.com/HelpDesk/Archiver.asp? Threadid = 8587 thanks to the author 2010-09-29 8:00:53 Let's take a simple look at how the SQL Server Index works. We will not talk about the index concepts. Clustered index: (Figure) Let's look at figure A, the structure of the clustered index.The data page is the place where the data is a

MySQL index details, MySQL index detailsI. Introduction to index basics 1.1 In MySQL, indexes are also called keys. They are a data structure that the storage engine uses to quickly find records. Indexes are critical to good performance. Especially when the amount of data in a table increases, the impact of indexes on performance becomes more and more important.

Learning MongoDB 8: MongoDB index (index restrictions) (2), mongodb IndexI. Introduction In the previous article, we introduced basic index operations through db. collection. the createIndex (keys, options) syntax creates an index. We will continue to introduce the restrictions of geospatial indexes and indexes, so tha

Analysis of Index Condition Pushdown (under the ICP Index Condition) and Multi-Range Read (MRR Index Multi-Range lookup) query optimization in MySQL, Source: http://www.cnblogs.com/wy123/p/7374078.html(The Source retained is not the right of original works. My work is far from reaching this level, just to link to the original article, because some possible error

Clustered index, nonclustered index, nonclustered unique indexWe all know that establishing an appropriate index can improve query speed and optimize queries. First, whether a clustered or nonclustered index is a B-tree structure . The clustered index matches the pr

Index range scan ): 1. for unique index, if the where condition is followed by 2. For none unique index, if the where condition is followed by =,>, 3. For composite indexes, if the bootstrap column of the composite index appears after the where condition, index range scan

[Index] basic knowledge of joint index and joint index 0. Preparation Suppose we have the table user (id, name) Column 1. What is composite index? We know that you can index a single column (such as id) of a table,For multiple columns (combination of id and name, or, name an