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strategy. The Red box section will be the focus of this article:Preliminary Knowledge-treeruleBefore describing how the SQL optimizer works, it is necessary to first introduce two important data structures: tree and rule. I believe that no matter what the SQL optimizer knows, you certainly know the concept of SQL syntax tree, the SQL syntax tree is the SQL statement after the compiler will be parsed into a tree structure. This tree contains a number of node objects, each with a specific data ty

Os._exit () and Sys.exit ()Os._exit () vs Sys.exit ()OverviewPython's program has two exit methods: Os._exit (), Sys.exit (). This article describes the differences and choices between the two approaches.Os._exit () will terminate the Python program directly, and all subsequent code will not continue to execute.Sys.exit () throws an exception: Systemexit, if the exception is not captured, the Python interpreter exits. If there is code to catch this exception, the code will still execute. Catchin

Special variables:$?: The execution result of the previous command returns a value of 0-255,0 for execution success, and other values indicate unsuccessful execution$!:shell PID of the last running background processPID of the $$:shell itself$: Script file path itself file name;$#: The number of script parameters;$*: all parameter lists. If "$*" is enclosed in "" ", output all parameters in the form of" $ $ ... $n "[Email protected]: all Parameters li

Org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest (invocablehandlermethod.java:132 ) at Org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle ( SERVLETINVOCABLEHANDLERMETHOD.JAVA:104) at Org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod ( requestmappinghandleradapter.java:749) at Org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleIn

1MariaDB [zabbix]>Selectauthentication_type from config;2+---------------------+3| Authentication_type |4+---------------------+5|2|6+---------------------+7 1RowinchSet (0.00sec)8 9MariaDB [zabbix]> Update config Set authentication_type =0 ;TenQuery OK,1Row affected (0.00sec) OneRows matched:1Changed:1Warnings:0 A -MariaDB [zabbix]>Selectauthentication_type from config; -+---------------------+ the| Authe

, which represents the balance on the card. mN=0 indicates the end of the data.Output for each set of inputs, outputs a line that contains an integer that represents the smallest possible balance on the card.Sample Input 1 50 5 10 1 2 3 2 1 1 2 3 2

1. This method is reproduced tohttp://blog.csdn.net/lt_java13/article/details/788146762. Remove the Api-ms-win-crt-runtime-l1-1-0.dll from the C:\Windows\SysWOW64.3. Reinstall Api-ms-win-crt-runtime-l1-1-0.dll (In fact this is VC redit.exe inside)4. Install VC Redit.ext Solu

classifies IP addresses according to TCP/IP ABCD, all 0 and 1 CIDR blocks are not allowed to be used to avoid ambiguity. this type of environment is called classful. in this environment, the subnet mask is valid only in the defined vro, And the mask information cannot reach other vrouters. for example, rip-1 does not contain mask information during route broadca

1. Create a simple script variable:Vim variable2. Modify the contents as follows:#!/bin/SHEcho "number:$#"Echo "scname:$0"Echo "First : $"Echo "second:$2"Echo "Argume:[email protected]"Echo "Show Parm list:$*"Echo "Show Process id:$$"Echo "Show Precomm stat: $?"3. Execute the Script./variableThe meaning of some parameters in a Linux shell script: $# is the number of arguments passed to the script. The name

Original URL: http://www.cnblogs.com/fhefh/archive/2011/04/15/2017613.htmlThe meaning of shell variable $#,[email protected],$0,$1,$2 in Linux is explained:Variable Description:$$The PID of the shell itself (ProcessID)$!PID of the Shell's last running background process$?End code of the last Run command (return value)$-Flag at a glance using the SET command$*All parameter lists. such as "$*" in the Case of

Original URL: http://dadekey.blog.51cto.com/107327/119938let's start by writing a simple script that will explain the meaning of each variable after execution .# Touch Variable# VI VariableThe script reads as follows:#!/bin/shecho "number:$#"echo "Scname:$0"echo "First: $ $"echo "Second:$2"echo "Argume:[email protected]"echo "Show Parm list:$*"echo "Show Process id:$$"echo "Show Precomm stat: $?"Save Exit assigning script Execution Permissions# chmod

#!/bin/bash#Created by Ley on 2014-11-14#Testing the Paramtersecho "The Compleate list is%s\n" "$$"echo "The Compleate list is%s\n" "$!"echo "The Compleate list is%s\n" "$?"echo "The Compleate list is%s\n" "$*"echo "The Compleate list is%s\n" "[Email protected]"echo "The Compleate list is%s\n" "$#"echo "The Compleate list is%s\n" "$ $"echo "The Compleate list is%s\n" "$"echo "The Compleate list is%s\n" "$ $"the meaning of shell variable $#,[email protected],$

In Oracle, if the absolute value is less than 1 decimal, only the value after the decimal point is displayed, and 0 in front of the decimal point is ignored, for example: 0.1 is displayed as. 1 in Oracle.How to resolve this type of problem:x=0.2To_char (' fm9999990.9999 ', x) output value is 0.2But now there is a problem, if it is x=10, then the display will be 1

Implements a 0 or 1 operation on a specified bit (for example, Nth bit) of a 8bit data (unsigned char type), and holds the other bit invariant # include The C language implements 0 or 1 operations on a specified bit (for example, Nth bit) of a 8bit data (unsigned char type) and keeps the other bits intact

To find the root of the equation ax^2+bx+c=0, consider respectively: 1, there are two unequal real roots 2, there are two equal real roots # include "C language" to find the root of the equation ax^2+bx+c=0, respectively, consider: 1, there are two unequal real roots 2, there are two equal real roots

determine whether an optional type has a value, which is used in the IF whilevar str:string? = "Renhairui"If var tmp = str{println (TMP)}implicitly optional type any existing type behind add! Represents an optional typeDifference:Int! Accept int values and nilint can only accept int valuesint and Nil accepted but forced to parseFunction: Used to define variables that are not re-converted to nil after assignmentYou also need to determine if let temp = name {}type alias typealias typealias Counte

My error message here shows:org.apache.ibatis.binding.BindingException: Parameter ‘reqUsername‘ not found. Available parameters are [0, 1, param1, param2]Cause: When there is only one parameter, mapper can not use @param, but when there are multiple arguments, use @param.The original code: @Select("select * from tz_user where " + GlobalConfigure.USER_AUTH_SQL_SUFFIX) ListChange to: @Select("select

Issue: After installing Python successfully, the command line failed to start, prompting Api-ms-win-crt-runtime-l1-1-0.dll to be lost.Solution: Baidu Search a solution, choose to install VC.Download link https://www.microsoft.com/zh-cn/download/details.aspx?id=48145Note: You need to first delete this file in the system, my file specific path: C:\Windows\SysWOW64 directory.Then run the download of the VC exe