teradata index

Summary of causes of index failure in Mysql and summary of index failure in mysql Http://blog.csdn.net/hehexiaoxia/article/details/54312130 When performing queries in a database, you often find that the query is slow, but you have already created an index on the column. After research, we found that the index fails i

1, WHERE clause in the query conditions are not equal to the number (where column!= ... ), MySQL will not be able to use the index2. Similarly, if a function is used in the query condition of the WHERE clause (for example: Where day (column) = ... ), MySQL will not be able to use the index3. In a JOIN operation (when data needs to be extracted from multiple data tables), MySQL can use the index only if it has the same data type as the primary key and

@parent =left (NEWID (), 40)EndInsert Mytesttable (id,parent) VALUES (@id, @parent)Select @[email protected]+1EndGoStep two, do not establish any index query tests/* Query when index is not established */DECLARE @beginTime datetime =getdate ()DECLARE @elapsedSecond int =0SELECT * from mytesttable where parent= ' dd7d9f34-3a9c-43ca-836b-f2babd78ce70 ' and id= ' 103ace5c-7 'Select @elapsedSecond =datediff (m

Mysql database index and mysql Index Today, let's talk about some of the indexes of the Mysql database. I think everyone knows what indexes can do? It is inevitable that data tables are quickly searched, especially those databases with millions of rows without indexing. Do you want to test your patience? Mysql has a variety of storage engines, which are bound to be different. For example, MyISAM is a B + Tr

MongoDB query, index and aggregation, MongoDB, and index aggregation Initialize the mongodb Database > Use dengswitched to db deng> db. createCollection ("jingdong") # No parameter {"OK": 1}> show collectionsjingdongsystem. indexes> userdoc1 = ({"user_id": 1, "name": "cloud", "state": "active", "actor": "user ", "e-mail": "test@qq.com", "VM_num": 2, "time": [{"date": "", "hour ": "53 53 PM"}]})> userdoc2 =

Linux index nodes and values (essential), and linux index nodes Audience, [Root @ luozhonghua aaa] # ls-l test. c-Rw-r --. 1Root 3 Aug 1 test. c # check that the index node value of the original test. c file in bold 1 is 1, that is, each file is unique when it is generated for the first time. [Root @ luozhonghua aaa] # ln test. c test1.c # Hard link file test1.c

.jpg "title=" 5.png " alt= "Wkiol1sm7ztd3bkzaaow_trwr6o878.jpg" width= "650" style= "Padding:0px;margin:0px;vertical-align:top;border: none; "/>T1 full table scan, T2 range Index Scan3. Non-unique index in T2.A1 and t1.a3650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M00/56/C3/wKiom1SM73myy97bAAPeTdOSTNU819.jpg "title=" 6.png " alt= "Wkiom1sm73myy97baapetdostnu819.jpg" width= "650" style= "Padding:0

where t1.a3=t2.a3 and t2.a1= ' www ';Select t1.a1,t2.a1 from t1 join T2 using (A3) where t2.a1= ' www ';Let's start withSelect t1.a1,t2.a1 from T1,t2 where t1.a3=t2.a3 and t2.a1= ' www ';TestExplain plan for select t1.a1,t2.a1 from T1,t2 where t1.a3=t2.a3 and t2.a1= ' www ';SELECT * from TABLE (Dbms_xplan. DISPLAY);1, do not build any index650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/56/C0/wKioL1SM7rPiO8jSAAN0dADWmzI552.jpg "title=" 3.png " alt= "Wkiol1sm7rpio8jsaan0dadwmzi552.jpg

[Daily] mysql index usage test and mysql index test 1. index is a data structure that helps MySQL efficiently obtain data. It can be understood as "sorting the data structure in order", outside of the data, the database system also maintains data structures that meet specific search algorithms. These data structures reference (point to) data in a certain way, so

In mysql5.6.19, The subquery cannot use the index. mysql5.6.19 Index The table structure is simple. Create table 'oplogs '('Id' int (10) unsigned not null AUTO_INCREMENT,'Kind' varchar (45) not null default '','Op' varchar (100) not null,'User' varchar (25) not null default '','IP' varchar (16) not null default '','Updatetime' timestamp not null default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,Primary

1. Parse tables and indexes (analyze does not rebuild the index )Analyze table TableName COMPUTE statisticsEquivalent to analyze table TableName compute statistics for table for all indexes for all columnsStatistics for table exist in views: User_tables, All_tables, Dba_tablesStatistics for indexes are present in views: User_indexes, All_indexes, dba_indexesStatistics for columns are present in views: User_tab_columns, All_tab_columns, Dba_tab_columns

If there is a clustered index and the lookup column is not in the key column of the nonclustered index and the RID lookup bookmark is used in a table that does not have a clustered index, it may be because the overhead is too large to cause some queries to directly perform table scan clustered index all the data is in

Sometimes a long character column needs to be indexed, which will make the index larger and slower. One policy is to simulate hash indexes. But sometimes this is not good enough, then? Generally, you can index the first few characters instead of all values to save space and improve performance. This reduces the size required for the index, but also reduces the s

The index creation rules for mysql optimization and the index Optimization for mysql The data structure commonly used for indexing is B + tree.. The structure is as follows: For example, it is a B + tree. For the definition of B + tree, see B + tree. Here we only talk about some key points. The light blue block is called a disk block, each disk block contains several data items (in dark blue) and pointers

This article is applicable to the reading references of the attacker who has some in-depth knowledge about database indexes. We are easy to understand clustering index scanning and table scanning, but it is not easy to understand non-clustered index scanning. This is often confusing for beginners, the reason is that there is no need for non-clustered index scanni

1, where the query conditions in the sentence is not equal to the number (where column!= ...) ), MySQL will not be able to use the index 2. Similarly, if a function is used in the query condition of the WHERE clause (for example, where day (column) = ...). ), MySQL will not be able to use the index 3, in the join operation (need to extract data from multiple data tables), MySQL can only use the primary key

MongoDB supports 2-D geo-information indexing. It is designed to carry out location-based queries in the mind, such as "Finding n places nearest to my location." It can also efficiently handle additional query conditions, such as "Finding n museums nearest to my location". To be able to use this index, you need to set a field in your object that is either a child object or an array of the first two elements x,y coordinates (or y,x-as long as it is co

Preface: In the development phase, it is difficult to always create the appropriate indexes on the appropriate columns. So the index you created at first may be invalid, and you need to find these invalid indexes. In general, when a query executes, the SQL Server optimizer chooses the most appropriate index to perform, and when no suitable index is found, the op

Tags: Table database capability effect int sha ble mysq typeThe MySQL database provides two types of indexes, and if not set correctly, the efficiency of the index is compromised but the problem is completely unknown. [C-sharp]View PlainCopy CREATE TABLE Test ( ID INT not NULL, Last_Name CHAR (+) not NULL, First_Name CHAR (+) not NULL, PRIMARY KEY (ID), INDEX name (last_name,f

Lucene -- Field. Store (storage domain options) and Field. Index (Index options), external efield. storeField. Store. YES or NO (storage domain option) Set "YES" to indicate that the content in this field is completely stored in the file for text restoration. If NO is set, the content of this domain is not stored in the file, but can be indexed. At this time, the content cannot be completely restored (doc