explain gigabytes

interpreting the Key_len in the explain implementation plan A column in the explain execution plan Key_len is used to indicate how many bytes are in the selected index length in this query, and we can often use this to determine how many columns of the federated index are selected. Here Key_len the calculation rule of size is: Generally, Key_len equals the byte length of the indexed column type, for exampl

Overview We know that the advantage of the simple factory model is to remove reliance on the client and the specific product, which is a violation of the "open-close principle"; The factory method pattern overcomes the drawbacks of the simple factory model, putting the product creation into a specific factory class, each of which is responsible for generating a product. But in practice, a factory class that only creates a single product is very rare, a general factory class will be responsible

, we found in the new station SEO scheme inside, the site title of the location and writing for site keywords and site rankings have a lot of help, then we should write their own website title, Front Baidu search engine and Google search engine has clearly explained the site title writing principles expressly, the following Nanning SEO small set to show you how to locate the site title of the basic ideas. 　　 We all know that Ma Yun is directly using robots.txt Baidu's search engine

Filters | detailed | repeat Many friends understand the "repeat edge pixels" and "retrace" in the "Undefined region" option of the substitution filter. Below I have to do a more detailed diagram explanation, for friends to refer to. Description Duplicate edge pixels are an option that is part of the set undefined area. It is related only to undefined regions (areas outside the selection). Notice the meaning of "edge" in "repeat edge pixels" while observing. I'm making a horizontally moving

|+----------------+-----------------+--------------------------------------------------------------+1 row in Set (0.00 sec)Use explain to analyze whether a hit index[SQL]View PlainCopy mysql> explain select * from user where username = ' a '; +----+-------------+-------+------+---------------+------------+---------+-------+------+-------------+ |ID |Select_type |Table | type | possible_keys |Key |

A lot of friends in the tuning with MySQL will certainly use the explain to see the execution of the SELECT statement, here is a brief introduction to the results of the meaning of the two columns.1 Type column The official saying that this column represents the "type of access", and more commonly, the way MySQL finds the data rows needed. One is to introduce the worst from the most efficient to the best: all this is called a full-table scan, and no i

Tags: MySQL query statement select explain and practiceSelect statement execution Process:START ———— >from------>where (SELECT, appropriate line)--------->group by (grouping)---------->having (filtering the grouping) ———— >order by ( Sort) ———— >select (projection, suitable field) ———— >limit ———— >end ResultSelect Single-Table query: DISTINCT: Data de -duplication: Select DISTINCT gender from students;Variables:mysql server itself built-in vari

Label:Qt5.5.0 use MySQL to write small software source code to explain---customer information registration form One person feels relatively simple and small software. Here is how to write how to publish packaging to introduce it! Download the MySQL library file link first: Http://files.cnblogs.com/files/xiaobo-Linux/mysql.zip Paste the two files into the QT directory \qt5.5.0\5.5\mingw492_32\bin folder directly (path according to your own settings) ca

MySQL Execution plan parameters detailedTurn http://www.jianshu.com/p/7134286b3a09In the MySQL database, you can view the execution plan of the query statement by adding "EXPLAIN" or "DESC" keyword in front of the SELECT query statement, and analyzing the execution plan is an important means of optimizing slow queries. Such as:EXPLAIN SELECT * FROM school; DESC FROM school;Execution Result:Execution plan parameters. pngThis is followed by a simple

A lot of friends in the tuning with MySQL will certainly use the explain to see the execution of the SELECT statement, here is a brief introduction to the results of the meaning of the two columns.1 Type column The official saying that this column represents the "type of access", and more commonly, the way MySQL finds the data rows needed. One is to introduce the worst from the most efficient to the best: all this is called a full-table scan, and no i

MySQL Explain (Execution Plan), mysqlexplain Today, database operations are increasingly becoming the performance bottleneck of the entire application, especially for Web applications. Concerning the database performance, this is not just something that DBAs need to worry about, but it is something that our programmers need to pay attention. When designing the database table structure and operating the database (especially the SQL statements used in t

The specific meaning of the return value of the performance test of the explain SQL statement the specific meaning of the return value of the performance test of the explain SQL statement is as follows: mysql> explain select * from table; + ---- + ------------- + ------- + ------ + ------------- + ------ + --------- + ------ + ------- + | id | select_type | table

PHP automatically adds a bom header when downloading files, explains the BOM header, and removes the bom header ,. How to automatically add a bom header and explain the BOM header and remove the bom header when downloading a PHP file? First, you need to understand what is the bom header? How to automatically add bom headers and explain BOM headers and remove bom headers when downloading files in Win PHP, T

An error occurred while reading a regular expression on the webpage. Let's take a look at the error. It is best to explain the meaning of each symbol. I am learning an example of a regular expression on the webpage, and an error has occurred. Let's take a look at the error. It is best to explain the meaning of each symbol. the div tag is being extracted and the content with the ID of PostContent is stored i

Briefly:You can use the EXPLAIN or DESC keyword to simulate the optimizer executing SQL query statements to know how MySQL handles your SQL statements. This can help you analyze the performance bottlenecks of your query statement or table structure.With the explain command you get:1. Reading Order of Table2. Operation type of table read operation3. Which indexes can be used4. Which indexes are actually used

EXPLAIN your SELECT query The EXPLAIN keyword helps you know how MySQL processes your SQL statements. This helps you analyze the performance bottleneck of your query statement or table structure.The EXPLAIN query results also show you how your index primary key is used and how your data tables are searched and sorted ...... And so on.SELECT one of your SELECT st

MySQL explain Execution Plan OptimizationExplain execution plan Introduction to MySQL optimization: First discover the problem (slow query, profile) If indexes are used and no indexes are used, you can quickly find data by using indexes. What is an index (an index is a data structure that is sorted for quick search) Manage indexes (view, create, and delete indexes) The data structure of the index itself (B-TREE structure and clustering structure

Explain shows how MySQL uses indexes to process SELECT statements and join tables. Can help select better indexes and write more optimized query statements.Using the method, add explain to the SELECT statement:Such as: Explain select surname,first_name form a b where a.id=b.id Explanation of the Explain

Explain syntax: Explain select ... from ... [Where ...] For example: Explain select * from news; Output: +--+ ————-+ ——-+ ——-+ ——————-+ ——— + ——— + ——-+ +--+ ——-+| ID | Select_type | Table | Type | Possible_keys | Key | Key_len | Ref | Rows | Extra |+--+ ————-+ ——-+ ——-+ ——————-+ ——— + ——— + ——-+ +--+ ——-+ The following is an understanding of each property:

 DB2 The explain table for the SQL execution plan does not exist by default, open DB2 command line, CD to the following directory C:\Program Files (x86) \ibm\sqllib\misc>lsDb2autobackuppolicy.xsd db2evmonpkgcache.xsd db2monroutines.xsd db2schemaannotation.xsl Db2adminV8.exe Db2uext2.v2Db2autoreorgpolicy.xsd db2evmonuow.xsd db2optprofile.xsd EXPLAIN. DDL DB2AUDIT.DDL WLMEVMON.DDLDb2autorunstatspolicy.xsd