explain gigabytes

If you want to analyze a performance problem with a SQL, you usually have to look at the SQL execution plan to see if there is a problem with every step of the SQL execution. If a SQL is normally performed well, but one day suddenly performance is poor, if the system resources and blocking reasons, then the basic can be concluded that the implementation of the plan. Understanding the execution plan is a prerequisite for SQL optimization. SQL optimization here refers to the positioning of the SQ

Explain shows how MySQL uses indexes to process SELECT statements and join tables. can help you choose better indexes and write more optimized query statements.Using the method, add explain to the SELECT statement before you can: Such as: Copy Code code as follows: Explain select Surname,first_name form a,b where a.id=b.id Explanation o

Explain shows how MySQL uses indexes to process SELECT statements and join tables. can help you choose better indexes and write more optimized query statements.How to: Add explain before the SELECT statement. such as EXPLAIN SELECT * from ' users ' Explanation of the Explain column:Table shows how the data in this row

To demonstrate the effect, let's start by creating a record with 2 million documents. (My own computer took about 15 minutes to insert the completed.) If you want to plug in more documents It's okay, just be patient and wait. ） 1 for (Var i=0;i After MongoDB 3.0, the return and use of explain has changed a lot with the previous version, the excellent feature after 3.0 and the 3.0.7 version We are currently using, this article is only for the

Explain and IndexExplain there are three modes, namely: Queryplanner, Executionstats, Allplansexecution. In the reality development, the common executionstats pattern, this example analyzes this mode.> db.createcollection ("Person"){"OK": 1}> for (var i=0;i... db.person.insert ({"Name": "Ryan" +i, "age": i})... }Writeresult ({"ninserted": 1})> Db.person.find ({"Age": {"$lte": +}}). Explain ("Executionstats"

Label: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 'a ',' B 'WHERE' a '. ' id '=' B '. ' id ' Explanation of the EXPLAIN column: col

In MySQL, you can use the explain command to see how a query statement is executed, using a method Example: Explain + query statementExample: Explain select * FROM User_infoA few important field descriptions:Table: Which data table is associated with this query operationType: Connection query operation types, generally according to the index query is const, if th

In git, Please enter a commit message to explain why this merge is necessary., gitmerge Please enter a commit message to explain why this merge is necessary. Enter the submitted message to explain why this merge is necessary. Git sometimes encounters this interface when pull or merge branches. You can skip this step (Step 3 or 4). If you want to enter an exp

Use the EXPLAIN keyword to check SQL statement efficiency Description You can use the explain command to understand how mysql processes statements and analyze the performance bottleneck of queries or table structures. Through expalin, we can get: 1. reading sequence of the table2. read operation type of the table3. which indexes can be used?4. which indexes are actually used?5. Reference between tables6. T

Who can explain in detail the execution process of $ a10; $ B $ a -- + -- $ a; in PHP? When I read Gao luofeng's book "elaborate on PHP", I found {code ...} if the above logic is used, add {code ...} can anyone tell us the detailed execution process of this code? Who can explain in detail the execution process of $ a = 10; $ B = $ a -- + -- $ a; in PHP? When I read Gao luofeng's book "elaborate on PHP", I

To explain the SQL Server Transaction log records, we all know that in the full recovery mode, SQL server records the operations performed by each firm and these records are stored in the transaction log, some software will use transaction logs to read operation records and recover data. For example, how can I view Transaction log records and what are recorded in logexplorer? Enable To explain the SQL Serv

Syntax format:EXPLAIN tbl_nameOr:Explain select select_optionsThe EXPLAIN statement can be used as a synonym for DESCRIBE, or used to obtain information about the SELECT statement to be executed by MySQL.The EXPLAIN tbl_name syntax is the same as DESCRIBE tbl_name or show columns from tbl_name.When the keyword "EXPLAIN" is used before a SELECT statement, MYSQL ex

I would like to explain the importance of manual experiments. Sometimes a person may have a lot of ideas, or you may have an idea when you see others' articles, or, if you want to verify others' opinions, you need to manually perform experiments to verify them. The idea is everywhere. For example, if I delete a piece of data, can I use the transaction log [fn_dblog] ()? restore him I would like to explain

Which of the following heroes can explain the principles and applications of php Cache Technology to the younger brother system? Thank you! Which of the following heroes can explain the principles and applications of php Cache Technology to the younger brother system? Thank you! Reply content: Which of the following heroes can explain the principles and appli

Foreach: In PHP, how does the result of the foreach loop explain the output principle? : In PHP, how does the result of the foreach loop explain the principle of the output result? The code is as follows:;} foreach ($ arras $ value) {echoValue:. $ value. lt; In PHP, how does the result of the foreach loop help explain the principle of output results?The code is

Please help me explain, multi-table join, I do not understand, thank you SQLcodeselect * from (selectbookid, count (bookid) asdegreefromtb_borrowgroupbybookid) asborrjoin (selectb. *, c. nameasbookcasename, p. pubname, t. typ, please help me explain. multi-table join queries are not easy to understand. thank you. SQL code select * from (select bookid,count(bookid) as degree from tb_borrow group by b

C # software Development engineer, stressed I want to engage in B/s, want to engage in js,css,html, but also on the Web back-end programming is not interested. This article is to stand in the frame of view to analyze the similarities and differences between b/s and C + +, think b/S and C/s is only the difference between the display layer, I also listed a simple example, also never deny B/s inside a web design (including js,css,html), At the same time, the purpose of writing this article is to t

How to automatically add BOM header and explain BOM header and get rid of BOM header when PHP download file, PHP download files automatically add BOM header, first of all to find out, what is the BOM header? When you save a text file in UTF-8 format with a program such as Notepad under Windows, Notepad adds several invisible characters (the EF BB BF) to the file header, which is the so-called BOM (Byte order Mark). In the Utf-8 encoded file, the BOM

Hive's explain command, which displays the execution plan for the SQL query.The hive query is transformed into a sequence phase (this is a forward-free graph). These stages may be mapper/reducer stages, or Metastore or file system operations, such as move and rename phases.ExampleHive> explain >Select* from student > by age;1. Abstract syntax tree for queries. "I use hive-0.13, not s

understood, but some people are particularly difficult to understand what you are saying.Idealism tells us not to find someone else's fault, first to find their own fault. So I tried hard to find, finally found, is my ability to express. The expression of the positive hero must reach the realm of Bai Juyi, to write the illiterate old can read the poem. Gradually became the words of the TB, the use of the most idiotic interpretation of all people, and develop bad habits, others do not understand