• C note 04 ﹣ operator


    operator An operator is a symbol that tells the compiler to perform a specific mathematical or logical operation. C language has built-in rich operators, and provides the following types of operators: Arithmetic operator Relational operators Logical operators Bitwise Operators Assignment Operators Misc. Operators Arithmetic operator The following table shows all the arithmetic operators supported by […]

  • Mongoose series 4 delete


    findOneAndDelete() Model.findOneAndDelete(filter[, options][, callback]) Parameter 1: filter The query statement is the same as find() Parameter 2: Options sort: if the query criteria finds multiple documents, set the sort order to select which document to delete. select/projection: Specifies the field returned. rawResultIf it istrue, the native result from mongodb is returned. Parameter 3: callback No […]

  • Output control of SAP SD basic knowledge


    Output control of SAP SD basic knowledge   1、 Output type of sales   Output is a communication method used to exchange information with business partners and systems. We can set the output for different sales documents such as quotation, order, delivery order and invoice. We can also set the output to confirm that it […]

  • What are the differences between Vue’s v-show and V-IF?


    v-ifThe event listener and subcomponents of the condition block will be destroyed and rebuilt during the switching process. If the initial condition is false, nothing will be done. The module will not be rendered until the condition is true for the first time.v-showJust switch based on CSS, no matter what the initial condition is, it […]

  • Nginx configuration: read custom header + compose and condition + modify response body + domain name redirection


    demand Without modifying the code, modify the response body to get the expected value when nginx forwards the request. The request has 2 unique features: url:/aaa/bbb/ccc/ddd Custom header (version sensitive):System-Version: proDifferent versions will request the same URL under the same server Tip: the main reason for this is the online management and control. After the […]

  • Performance tuning of SQL tuning


    Syntax based optimization and simple query conditions. Syntax based optimization refers to the selection of words and the order of writing in SQL statements without considering any non grammatical factors (such as index, table size and storage). general rule In this section, I’ll look at some general rules that you need to pay attention to […]

  • Angular 2 ViewChild & ViewChildren


    Read the latest tutorial of angular 6 / rxjs, please visit the front-end fairy Road ViewChild Viewchild is an attribute decorator used to get matching elements from the template view. The view query is completed before the ngafterviewinit hook function is called, so in the ngafterviewinit hook function, you can get the elements of the […]

  • Redis dig deep del


    Command Brief Usage: DEL key [key …] Delete one or more given keys. Keys that do not exist are ignored. Return value: Number of deleted keys. Example: redis> SET name huangz OK redis> DEL name (integer) 1 #Delete a key that does not exist redis> EXISTS phone (integer) 0 Redis > del phone failed, no […]

  • Field type (uniqueidentifier) problem


    Environment: SQL 2016; Statement select * from a where PID = joid In the above query statement, where PID = join condition, the field type of PID is varchar (50) and the field type of join is uniqueidentifier. This writing method has no problem in the (sql2012) library before upgrade, but it will report an […]

  • Cyclic structure


    Cyclic structure Loop: let programRepeatedlyExecute the same code*Three elements: 1. Loop condition: the condition for loop * to continue * to execute For example: number of turns < 3 2. Cyclic variable: the variable used for comparison in the cyclic condition For example: number of turns How many changes do you make each time The […]

  • The implementation of searching in mongodb using PHP


    The conditional operator is used to compare two expressions and get data from the mongodb collection.The condition operators in mongodb are:(>) greater than – $GT(> =) greater than or equal to – $GTE(< =) less than or equal to – $LTEMongodb uses the $regex operator to set the regular expression of the matching string, and […]

  • Bash tip: explaining the use of while and until loop commands


    In the bash shell of Linux,whileCompound command anduntilCompound commands can be used to loop the specified statement until false is encountered. Check the description of while and until in man bash as follows: while list-1; do list-2; done until list-1; do list-2; done The while command continuously executes the list list-2 as long as the […]