Tag:Null value

  • PGSQL implementation judges a null value field and modifies the NULL value to another value


    When using pgsql, if you want to get data whose fields are not empty or empty, you can use the following methods: 1. Not empty Select * From table Where id<>” Select * From table Where id!=” 2, is empty Select * From table Where id=” Select * From table Where ISNULL(id) If the field […]

  • Solve the problem that MySQL uses not in to contain null values


    be careful!!! select * from user where uid not in (a,b,c,null); This SQL does not return any results. To avoid null in the list of not in. In addition: – if NULL participates in arithmetic operation, the value of the arithmetic expression is null. (for example: +, -, *, / addition, subtraction, multiplication and division) […]

  • Solve the problem of null value in go language database


    This paper mainly introduces how to use the database/sql Library of go language to read null values from the database, and how to insert null values into the database. SQL is used here in this article NullString, sql. NullInt64, sql. Nullfloat64 and other structures. For the convenience of writing, I will use SQL for their […]

  • Why not use equals?


    In this article, we will summarize the differences between a.equals (b) and a.equals (b), and then make a small analysis of the source code. 1、 When the value is null: a. Equals (b), a is null, and a nullpointexception exception is thrown. a. Equals (b), a is not null, B is null, and false is […]

  • The road to big data – (I) data cleaning in algorithm modeling


    Author: mochau Source:Hang Seng light cloud community In the context of current big data, data processing accounts for a huge share. Just like a tomato made into a scrambled egg, it needs seasoning integration, vegetable cleaning, food processing, etc. before it can be released to production. No, it can be sent to the table. Here, […]

  • Add a “request lock” to the interface


    When developing back-end interfaces, we always want to simplify some non open interfaces and do not consider malicious attacks such as DDoS too much. However, when we went online, we found that some strange problems often troubled the students at the back-end, including frequent requests for the same parameters due to users’ multiple clicks on […]

  • Method for processing null value in SQL statement


    Do you care about null value when using database everyday? In fact, null value is a very special and interesting existence in the database. Let’s take a look at it together; When querying the database, if you want to know whether a column (e.g. user_age) is null, how to write the SQL query statement? Here’s […]

  • 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 […]

  • Kotlin null type safety and intelligent type conversion


    1、 Foreword < font face = bold > inClasses and interfaces in kotlinWe have talked about kotlin’sclass、InterfaceandExtension methodToday, let’s talk about kotlinEmpty type securityandSmart type conversion。 2、 Kotlin null type security 2.1. Empty type safety concept < font face = bold > there is no concept of empty type safety in the Java language, so […]

  • The system command operates the register to find a specific character in proc


    1、 void sd5_close_i2c_clk() { static int i2c_reseted = 0; if( !i2c_reseted) { i2c_reseted = 1; printf(“>>>>>>>date:%s>>>>>>>disable i2c clk.\n”,__DATE__); WRITE_DEBUG_LOG_TO_SDCARD(“>>>>>>>date:%s>>>>>>>disable i2c clk.\n”,__DATE__); /*disable i2c*/ system(“devmem 0xc0010014 32 0x0”); usleep(100*1000); /*pin mux*/ system(“cur=$(devmem 0xc00100B0);new=$(($cur|(0x03<<7)));devmem 0xc00100B0 32 $new”); usleep(100*1000); /*out put*/ system(“cur=$(devmem 0xc0070028);new=$(($cur|(0x03<<7)));devmem 0xc0070028 32 $new”); usleep(100*1000); /*close i2c clk*/ system(“cur=$(devmem 0xc0070008);new=$(($cur&(~(0x03<<7))));devmem 0xc0070008 32 $new”); } else { […]

  • [share] IOS development – the difference between the two common writing methods when judging whether the array is empty


    Some developers, when judging whether the array is empty, will write: if (array != nil) or if (array.count != 0) In fact, strictly speaking, these two writing methods are both under considered and unstable, and ignore a more common situation. First, let’s talk about the difference between the two. array == nil This means that […]

  • Talk about null coalescing operator in JavaScript


    Null merge operator (?) Is a logical operator that returns the right side of the operator (second parameter) only if the left side (first parameter) is empty or undefined. In all other cases, it returns the first parameter. The following two lines of test code output Hello and 132 respectively Therefore, as you can see […]