• English short sentences


    To work hard, but don’t try so hard, the beauty of the flowers, fruits are needed to process People are always like this. At last, they know how to cherish, but everything is scattered—— This is always the case, when it comes to appreciating the age, but everything is separated. If you want to be […]

  • Pandas’s handling of missing values


    Pandas uses these functions to handle missing values: Isnull and notnull: detect whether it is a null value, which can be used for DF and series Dropna: discard and delete missing values Axis: delete row or column, {0 or ‘index’, 1 or ‘columns’}, default 0 How: if it is equal to any, any value will […]

  • MySQL exercise


    1.Name of the person with the highest salary in each department Solution: 1. Ask for the highest salary of each department first SELECT e.deptno,MAX(e.sal) as maxsal from emp e GROUP BY e.deptno; 2. Take the results obtained in the first step as a temporary table SELECT e.deptno,ename,t.maxsal,e.sal from (SELECT e.deptno,max(e.sal) as maxsal from emp e […]

  • Linux note sharing 8: setting file permissions


    1、 Setting of document authority -rw-r–r– first-Is the file type(-Representative documents,dRepresentative directory,|Represents a soft link file) About the last nine rw- r– r– U owner Group G O others R is the read permission, W is the write permission, and X is the execute permission 1、chmod Permission to modify files Chmod [options] mode file name […]

  • SQL server uses join all to optimize or query speed


    For example: Master, test indicates that the user is the subordinate code of test. After test logs in, you can see the business under the name of test and the business of all subordinate agents. The structure of the related tables is as follows: The user table has about 100000 records |-uid-|-user-|—-site——| | 1 | […]

  • Microsoft IOS engineer Society


    Microsoft (China) Completed in 1 day, a total of 5 rounds, 5 engineers, different ranks, order, the whole English. One round: Let me introduce myself first. How to optimize the application time. 3. Whiteboard gives the first scenario: an email application, a simplified version of outlook, with only two tabs of message and contacts. It […]

  • Basic usage of Union and union all in MySQL


    In the database, the Union and union all keywords merge the two result sets into one, but they are different in terms of usage and efficiency. Union in MySQL Union will filter out duplicate records after table linking, so it will sort the generated result set after table linking, delete duplicate records and return the […]

  • The usage of Union and union all in SQL statements


    Union and join statements are very similar in SQL, but union has one restriction: the fields generated by two SQL statements need to be of the same data type, and the final result will see different data values. Format: [SQL statement 1] UNION[SQL statement 2] For example: Table store? Info And table Internet & sales […]

  • BSD system allows a user to log in and shut down


    cd  /usr/ports/security/sudo make install clean; visudo jxtm    ALL=(ALL)       NOPASSWD:/sbin/halt -pThis way jxtm can be added before the commandsudoTo executehalt– p, and no password is required. Add the last line to the user‘s. SHRC sudo /sbin/halt -p In this way, the jxtm account is automatically logged inShutdown了  

  • Running and debugging asterisk under FREEBSD


    1. Running Common Commands for Debugging . / asterisk & Start asterisk in the background . / asterisk – VVC starts asterisk and displays debugging information on the console as much as possible . / asterisk – R connects to the asterisk console Set verbose 9999 Set Print Details 2. Common commands under asterisk console […]

  • Understanding the use of all attributes in CSS3


    I. Compatibility The following picture: Compatibility is also good, except IE does not support, other browsers are basically green, at present, self-entertainment, intranet projects and anything can be used. 2. What is all for? All attributes are actually abbreviations of all CSS attributes, indicating how all CSS attributes are, but excluding unicode-bidi and direction. Why […]