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Cause: It's too slow to make count (*) statistics on the InnoDB table, so find a way to see if it's going to be faster. Phenomenon: First look at a few test cases, as follows First, the test on the Sbtest table Show CREATE TABLE Sbtest\g1. Row ***

Another example of "12c more consumption than 10g index back-table" case, colleagues in 12c run the buffer get is very high, but in 10g run a low buffer. Doubt whether the 12c optimizer has a problem. This 10g environment and 12c environment, the

First of all, MySQL Phantom read is not "a transaction within two times the same operation actually got a different result", because it is not possible at the RR isolation level using the Read VIEW/MVCC, the definition of this magic is more suitable

In versions earlier than 11gR2, when creating a table, the segment space is automatically allocated. There are several drawbacks to doing so: 1. space needs to be allocated during initial table creation, which naturally takes some time. If multiple

Oracle grouping and grouping functions 1. summation and averaging 1. What is a group function is the multi-row function we mentioned earlier. It is mainly used for table operations. Because only tables have multiple rows of data. The following uses

Translator: ye Jinrong (imysql # imysql.com), source: imysql.com, please reprint it. Cause: It is too slow to make count (*) Statistics on the innodb table, so try to see if you can hurry up. Symptom: Let's take a look at several test cases. 1. Test

In general, we can use the following four methods to get the execution plan of the target SQL:(1) explain plan command(2) Dbms_xplan bag(3) Autotrace switch in Sqlplus(4) 10046 eventsIn addition to the fourth method, the execution plan obtained by

Oracle automatically clears logs in the materialized view. Oracle determines when to delete the materialized view log based on the registration information on the base table of the Materialized View and the refresh of the materialized view. The

I think it's time to use string parameters to help us solve this situation, using string segmentation to divide a parameter into several parameters to solve. Let's take a look at the following example: Suppose you now give a list of product

ORACLE Advanced Function Application --Grouping functions 1, ROLLUP --Subtotal, total of statistical standard grouping and corresponding dimensions The Oracle GROUP BY statement also supports rollup and cube statements in addition to the most basic

Stored procedure procedure (proc)Database-programmability-stored proceduresTo create a new stored procedure:Create proc FirstprocAsSelect *from FenshuGoTo execute a stored procedure:Stored procedure-Right-executes stored procedureDECLARE @fanhuizhi

Query optimization Technology of databaseQuery optimization Technology of databaseDatabase system is the core of MIS, and online transaction processing (OLTP) and online analytical Processing (OLAP) based on database is one of the most important

First, unreasonable index design ----Example: The table record has 620000 rows, and the following SQL runs under different indexes: ----1. A non-clustered index was built on date Select COUNT (*) from the record where date > ' 19991201 ' and date 20

first, unreasonable index design ----Example: The table record has 620000 rows, and the following SQL runs under different indexes: ----1. A non-clustered index was built on date Select COUNT (*) from the record where date > ' 19991201 ' and date 20

People tend to get into a misunderstanding when they use SQL, it is too focused on whether the resulting results are correct, ignoring the possible performance differences between different implementations, which are particularly evident in large or

server| Index | Problem----When using SQL, people tend to fall into the myth that too much attention is paid to the correctness of the results, while ignoring the possible existence of different implementations Performance variance, which is

1. Determine if there are any injection points; and 1=1 and 1=22. Guess the table name is nothing more than the admin Adminuser user pass password and so on.and 0<> (SELECT COUNT (*) from *)and 0<> (SELECT COUNT (*) from admin)---Determine if the

This article introduces the detailed description of MySQL partition performance. For more information, see I, Partition concept PartitionAllows you to allocate multiple parts of a single table across file systems based on specified rules.

And exists (select * from sysobjects) // you can check whether it is MSSQL. And exists (select * from tableName) // determines whether a table exists. tableName indicates the table name. And 1 = (select @ VERSION) // MSSQL VERSION And 1 = (select db_

Script intrusion is very popular on the Internet, and the Script Injection Vulnerability is popular among hackers. Whether it's an old bird or a new dish, it will be fascinated by its great power and flexible moves! It is precisely because of the