how to improve query performance

Conceptif The index contains all of the data that satisfies the query, the index becomes the overwrite index (covering index), which is what you usually say does not require a table operation.Judging criteriawith explain, you can tell by the output

Oracle Table Partitioning details the concept and operation of partitioned tables from the following aspects: Table space and partitioned table concept table partitioning specific role table partitioning several types of table partitioning and how

Original address: http://blog.csdn.net/zwan0518/article/details/11972853Directory (?) [-] One query optimization 1 Creating an Index 2 Configuration of the cache 3slow_query_log Analysis 4 Sub-Library sub-table

Write in front: indexes have a critical impact on the speed of queries, and understanding indexes is also a starting point for database Performance tuning. Consider the following scenario, assuming that a table in the database has 10^6 records, the

Install on 1,mac (specify JAVA8)Install java8vim. base_profile file contents: Java_home=/library/java/javavirtualmachines/jdk1. 8. 0_162.jdk/contents/HomePath= $JAVA _home/bin: $PATHCLASSPATH=.: $JAVA _home/lib/dt.jar : $JAVA

OverviewChildren's shoes with MySQL know the need to build an index, but many people just stay in indexing to make the query faster However, in order to achieve this goal, it is very necessary to establish a scientific and rational index. Indexes

Now with the development of the Internet, the magnitude of the data is also exponential growth, from GB to TB to PB. The operation of the data is also more difficult, the traditional relational database can not meet the needs of fast query and

1, the difference between varchar and nvarchar?VARCHAR (n): variable-length, non-Unicode character data with a length of n bytes. n must be a numeric value between 1 and 8,000. Storage size is the actual length of bytes of input data, not n bytes.

Nowadays, Oracle databases are favored by more and more enterprises for their high reliability, security, and compatibility. Readers may wish to consider the following aspects to ensure the permanent performance of Oracle databases. PartitionBased

The database engine uses indexes to improve query efficiency and adds many optimization policies for indexes. However, there are also many details during the indexing process. If you ignore these problems, hard-built indexes may not be well applied,

The B + tree is a classic data structure generated by the combination of the Balance Tree and the binary search tree. It is a balanced search tree designed for disks or other direct access devices, in the B + tree The B + tree is a classic data

The explanation of mysql explain is clear.Of With the help of explain, you will know when to add an index to the table to use the index to search for records so that select can run faster.If the index is not properly used, you can run analyze table

Database objects Common: tables: basic database objects for storing data, composed of rows (records) and columns (fields) Constraints: series of rules for performing data verification to ensure data integrity View: Logical display of data in a table

DBA classic interview questions (1) 1: List several table join Methods: hash join, merge join, nest loop join (cluster join), and index join 2: no third-party tools, how to view the SQL Execution Plan set autotrace on if the following error occurs:

1. create and manage tables1. Create Table syntaxCreate table Name (column datatype [default expr] [, column...])Default Constraints2. Create a table using subqueryCreate table NameAsSelect * from u tableIi. modify a table1. Add a new columnOracle:

The following articles mainly describe the correct use of the MQT materialized query table in the materialized view of the DB2 database. If you encounter the application of the MQT materialized query table in the materialized view of the DB2

The following articles mainly introduce the correct use of MQT materialized query tables in the materialized views of DB2 databases, if you are a beginner in the practical application of the correct use of the MQT materialized query table in the

The following articles mainly introduce the basic tutorial of SQL coding optimization for the IBM DB2 database. The importance of such a specific query is that the more important the query is, you may need to optimize indexes by creating indexes. If

In daily use, the index we create is not a strategic index. It is precisely because a large number of redundant or useless indexes consume a large amount of storage space, resulting in low DML performance. Oracle In daily use, the index we create is

The advantage of parallel query is that it can process query jobs through multiple threads, thus improving the query efficiency. The SQL Server database provides the parallel query function for database servers with multiple CPUs to optimize the