Tag:Full table

  • A case of using union index

    Time:2021-2-22

    In practice, full table scanning is always avoided, so slow table scanning is avoidedsqlIndex on some fields in. The significance of index building is that the original operation of scanning and operation in the table is executed in the index to reduce the number of scanning rows in the table, so the query speed is […]

  • Oracle indexing and SQL optimization

    Time:2021-2-11

    Database index: The index has a single column indexOn compound index If a field of a table has a primary key constraint and a unique constraint, Oracle will automatically propose a unique index on the corresponding constraint column. Database index is mainly used to improve access speed. Construction principle: 1. Indexes should always be built […]

  • Index failure

    Time:2021-2-6

    Index is a very important chapter for MySQL. There are also many knowledge points in the index. If you want to master them thoroughly, you need to break them one by one. Today, let’s talk about the situations that will lead to index failure. Picture summary Full value matching (best index) explain select * from […]

  • A slow query optimization of MySQL

    Time:2021-2-4

    Recently, I met a slow query problem in mysql, so I checked it. Here is a summary of the related process. Positioning reasons First of all, I checked the slow query log of MySQL and found that such a query takes a long time (about more than one second) and scans a large number of […]

  • Step by step teaching you MySQL query optimization analysis

    Time:2021-1-29

    preface MySQL is a kind of relational database,Strong query function,High data consistency,High data security,Support secondary index. But the performance is slightly inferior to that of non relational database, especially for the data above one million level, it is easy to slow down the query. At this time, we need to analyze the reasons for the […]

  • Improve 30 SQL query optimization methods for 10 million level MySQL data

    Time:2021-1-26

    See what you use: 1. To optimize the query, we should try to avoid full table scanning. First, we should consider building indexes on the columns involved in where and order by. 2. Try to avoid judging null value of field in where clause, otherwise it will cause the engine to give up using index […]

  • Oracle database optimization skills (1)

    Time:2021-1-20

    Oracle database optimization skills (1) 1. Join order in where clause In Oracle database, the execution order of where clause isBottom upAccording to this principle, the connection between tables must be written before other where conditions, and those conditions that can filter out the maximum number of records must be written before other where conditions […]

  • Records an event in which a range query hits an index but does not use an index

    Time:2020-12-20

    cause There are two general indexes create in the main order table of production environment_ Time and debts_ notify_ Num, when these two conditions are used for filtering, both indexes are hit, but only debts is used_ notify_ Num, resulting in more query columns and slower queries. It looks like “the index hits, but the […]

  • SQL Server deleting database table by mistake

    Time:2020-12-14

    Not to mention the history of blood and tears, we used all kinds of stored procedures and settings described on the Internet, and finally solved them with third-party software, Premise: database full table backup, how to check the details of Du Niang, the software used is apexsqllog, the database is sqlserver2017, the next version has […]

  • New features interpretation | 8.0 new DML statement (Table & values)

    Time:2020-12-12

    Author: Yang TaotaoSenior database expert, specializing in MySQL for more than ten years. Good at mysql, PostgreSQL, mongodb and other open source database related backup recovery, SQL tuning, monitoring operation and maintenance, high availability architecture design, etc. At present, he works in akesheng, providing MySQL related technical support and MySQL related courses training for major […]

  • Million level database optimization

    Time:2020-12-7

    1. To optimize the query, it is necessary to avoid scanning the whole table as much as possible. First of all, we should consider building indexes on the columns involved in where and order by. 2. We should try our best to avoid judging the null value of the field in the where clause, otherwise […]

  • MySQL execution plan

    Time:2020-12-5

    Series articles: Range partition MySQL execution plan In the application scenarios of enterprises, in order to know how to optimize the execution of SQL statements, it is necessary to view the specific execution process of SQL statements to speed up the execution efficiency of SQL statements. You can use the explain + SQL statement to […]