db2 query optimization

Brief introduction With the increasing application of DB2, more and more database developers are confronted with the problem that the query is too complicated and the performance is difficult to be accepted in the process of project development. This article will mainly from a database developer's point of view introduces several commonly used methods to improve the performance of

Label:ORACLE : --Time Turn string To_char (sysdate, ' Yyyymmddhh24miss ') --String Turn time Select To_date (' 20140701125751 ', ' Yyyymmddhh24miss ') from dual--2014-07-01 12:57:51 --Query table SELECT * FROM all_tables WHERE table_name = ' {0} ' --Query column SELECT Aa.table_name as Tableename, Aa.column_name as ColName, NVL (Bb.comments, aa.column_name) as Coldesc From ( SELECT TABLE_NAME, COLUMN_NAME,

DB2 materialized view Mqts are based on a table defined by the query result, and the MQT contains data from one or more tables on which the MQT definition is based, and using MQTS can significantly improve the operation performance of the query. The views and mqts for the database are defined based on a query. The

In DB2, the sum function used to replace the count query is to calculate and sum the column values. The www.2cto.com count function accumulates the columns that meet the conditions and adds one when the conditions are met. The count function is commonly used to count the number of records meeting a certain condition. For example, count the number of boys in student in the student information table: [SQL] se

Mysql uses indexes for query optimization and mysql index Query Optimization The purpose of indexing is to improve the query efficiency. It can be analogous to a dictionary. If you want to query the word "mysql", you must locate t

1. mysql Paging query(1) Keyword: LIMIT beginindex, MaxRow(2) Example:The limit clause can be used to limit the amount of data returned by the SELECT statement, which has one or two parameters. If two arguments are given, the first parameter specifies the position of the first row returned in all data, starting with 0 (note not 1), and the second parameter specifies the maximum number of rows to return. For example:-- starting from Beginindex line,

Like fuzzy query for oracle, mysql, db2, and SQL server in Mybatis, mybatisdb2 Different database languages: SQL server, Oracle, mysql, db2'' There are too many database system types. To put it simply, ACESS is suitable for small websites. asp and MYSQL are recommended for new websites. SQL Server is suitable for medium-sized websites and PHP is recommended for

The paging query method for Oracle, SQL, and DB2 is different from that for paging query statements in Oracle and SQL, the following describes the differences between DB2 paging query and paging query in other databases. Oracle pa

Tags: using data SP C size r database SQL BSPaged query statements that are used in different databases:Current page: CurrentPagePage Size: pagesize1. Oracle DatabaseSELECT * FROM (select A.*,rownum rn from (query_sql) A) where Rn Note: query_sql is a query SQL statement.OrSELECT * FROM (select RowNum rn,id from TABLENAME where RowNum 2. Infomix DatabaseSelect Skip CurrentPage First pagesize * from TABLENAM

,neibuyonghu,reader,title from Tgongwen where fariqi> ' 2004-1-1 ' and fariqi4. The date column will not slow down the query speed because there is a minute or seconds inputIn the following example, there are 1 million data, 500,000 data after January 1, 2004, but only two different dates, the date is accurate to the day, before the data 500,000, there are 5,000 different dates, the date is accurate to the second.Select Gid,fariqi,neibuyonghu,reader,t

result set type returned by the subquery is a simple value. b) Single-row sub-query. The result set type returned by the subquery is 0 or one unit group. Similar to the scalar subquery, but may return 0 tuples. c) Multiline single-row subquery. The result set type returned by a subquery is a multi-tuple but has only one simple column. d) Table sub-

Materialized query tables using MQTS (materialized query tables, MQTS) The definition of an MQT is based on the results of the query. Mqts can significantly improve the performance of queries. This tutorial introduces Mqts, Summary tables (summary table), and staging tables, and shows you how to create and use materialized q