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SQL Optimization-logical Optimization-external connections, nested connections, and elimination of connections, SQL nesting 1) eliminate external connections ① External connection Introduction 1) left join/left outer join: LEFT OUTER JOIN The result set of left outer Join includes all rows in the LEFT tabl
MySQL View details of all current connections:Mysqladmin-u root-p ProcesslistMySQL view current number of connections (threads is the number of connections)Mysqladmin-u root-p Statusuptime:1047464 threads:22 questions:1494780 Slow queries:0 opens:31357 Flush tables:1 Open tables:1981 Queri Es per second avg:1.427MySQL shows which threads are runningList only the first 100: show Processlist;All listed: Show
We often use joint queries for two tables. Sometimes we use internal connections, full connections, and left and right connections. Is it very complicated? The following is a demonstration of their differences. First, there are two tables: CREATETABLEweather ( citycharactervarying(80)NOTNULL, temp_lointegerNOTNULL, temp_hiintegerNOTNULL, prcpr
on the connection condition using (department_id), but department_id = 40 There is no matching record in the Employees table. It is common sense that the record corresponding to department_id = 40 will be thrown. However, to save all records in the connector tables A matched record is used to save all records of the connected table. Of course, the value of this virtual record is null. --------------------------Natural join----------------------------- SQL> select * from employees
in the data, three times after the handshake, the client and the server began to transfer data officially. Ideally, once a TCP connection is established, the TCP connection is maintained until either side of the communication actively closes the connection. When disconnected, both the server and the client can initiate a request to disconnect the TCP connection, and the disconnect process requires a "four handshake" (the process is not fine, that is, the server and client interaction, the final
are as follows: Watermark/2/text/ahr0cdovl2jsb2cuy3nkbi5uzxqv/font/5a6l5l2t/fontsize/400/fill/i0jbqkfcma==/dissolve/70/gravity /center "> conditionalDescription: The unconditional results found above are filtered according to the conditions but here only can be used to indicate that you cannot use on the results are as follows: Summary The phrase is given to himself and to all the readers:In the future, understand a piece of things will be its ins and outs, and to summarize, so that the futu
TESTC C on (A.A=C.A);The results table is as follows:Three, outer connection:1. Left Outer connection outer JOIN or Ieft JoinThe left OUTER join is the addition of unmatched data from the primary table on the basis of the equivalent connection, for example:Notation One: SELECT * from TESTA a left OUTER JOIN TESTC C on (A.A=C.A);Notation Two: SELECT * from TESTA a left JOIN TESTC C on (A.A=C.A);Oracle-specific notation: SELECT * from TESTA A,TESTC C WHERE a.a=c.a (+);The results table is as foll
Original: https://www.cnblogs.com/gotodsp/p/6366163.html1. The relationship between the HTTP protocol and the TCP/IP protocol Long connections and short connections to HTTP are essentially TCP long connections and short connections. HTTP belongs to the Application layer protocol, which uses the TCP protocol at
General purchase of virtual host friends are familiar with the purchase, will limit the number of IIS connections, this side first from the general do not understand the code user perspective of IIS connectionsAs the name implies, the maximum number of connections that the IIS server can hold for a client request, which is exactly the number of "IIS Restricted connectio
Tags: Read connect ext ams in file according to request system passMySQL view maximum number of connections and modify maximum connections 1. View the maximum number of connectionsShow variables like '%max_connections% ';2. Modify the maximum number of connectionsSet GLOBAL max_connections = 200; The following article is mainly to introduce you to the MySQL maximum connection number of changes, we all know
Label:MySQL Maximum connection number problem In MySQL source code, the default maximum number of connections is 16384 {"Max_connections", Opt_max_connections,"The number of simultaneous clients allowed.", (gptr*) max_connections,(gptr*) max_connections, 0, Get_ulong, Required_arg, 100, 1, 16384, 0, 1,0}, Appear too many connections problem, at this time there is no way to conn
Tags: cat alter ash machine spfile term text CLI OracleIt is useful to look at the connection of the data, finish writing the program while testing the code side to see the release of database connections to help optimize the analysis of a robust system program. 1. View the current number of database connections Select COUNT (*) from v$process; --Current number of database
Tags: style http color using OS IO file dataWhat is a long connection?In fact, a long connection is relative to the usual short connection, that is, long time to maintain the client and the server connection state.The usual short connection operation steps are:Connect-"Data transfer-" close the connection;A long connection is usually:Connect-"Data transmission-" Stay connected-"data transmission-" Stay connected-"...-" close the connection;This requires a long connection in the absence of data c
Tags: program blank ext suse process Dalian param Connect UserRelationship between two parameters: Sessions=1.1*processes+5 The current summary of the statement, in view of the data connection is very useful, after writing the program while testing the code side to see the release of database connections to help optimize the analysis of a robust system program. 1.SQL code1.select Count (*) fromv$processSelect COUNT (*) from v$process where program= '
Tags: desc use div ons parameter. sql start ble ora The current summary of the statement, in view of the data connection is very useful, after writing the program while testing the code side to see the release of database connections to help optimize the analysis of a robust system program. 1.SQL code1.select Count (*) from v$processSelect COUNT (*) from v$process--current number of database
HTTP persistent connections and short connections are essentially TCP persistent connections and short connections. HTTP belongs to the application layer protocol and uses TCP protocol at the transport layer. 1. relationship between HTTP protocol and TCP/IP protocol HTTP persistent
0. TCP/IPTCP/IP is a protocol group that can be divided into three levels: Network layer, Transport layer and application layer.At the network layer are IP protocols, ICMP protocols, ARP protocols, RARP protocols, and BOOTP protocols.There are TCP protocols and UDP protocols in the transport layer.At the application level: TCP includes FTP, HTTP, TELNET, SMTP, and other protocolsUDP includes DNS, TFTP, and other protocols1. The relationship between the HTTP protocol and the TCP/IP protocolLong
The current summary of the statement, in view of the data connection is very useful, after writing the program while testing the code side to see the release of database connections to help optimize the analysis of a robust system program.1. SQL codeSelect COUNT (*) from v$processSelect COUNT (*) from v$process--current number of database connections2. SQL codeSelect value from v$parameter where name = ' processes 'Select value from v$parameter where
http long connections and short connections 1. The relationship between the HTTP protocol and the TCP/IP protocol Long connections and short connections to HTTP are essentially TCP long connections and short connections. HTTP bel
Discussion socket must discuss long and short connectionsConcept of one, long connection and short connection1, the concept of long connection and short connection: The former is the entire communication process, the client and server only with a socket object, long-term to maintain the connection of the socket; the latter is a new socket for each request, which closes the socket directly after processing a request. So, in fact, the difference between the length of the connection is: the entire
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