Tag:Null value

  • [Oracle] invalidation when the fields associated with the two tables are null during left join

    Time:2021-10-19

    The problem of invalidation when the fields associated with the two tables are null during Oracle left join Problem description TESTA subject score chinese 90 mathematics 30 English 9 100 TESTB subject score chinese 3 mathematics 79 English 99 120 If left join is used, the value 120 corresponding to the null value of testb […]

  • ThinkPHP 5 model usage history – replication

    Time:2021-9-12

    Series articles: ThinkPHP 5 model usage history – inherit first and then extend ThinkPHP 5 model usage history – replication ThinkPHP 5 model usage history – global definition ThinkPHP 5 model usage history – ide friendly ThinkPHP 5 model usage history – Single Responsibility ThinkPHP 5 model usage history – sorting code ThinkPHP 5 model […]

  • The. Net core handles webapi JSON and returns annoying null and empty

    Time:2021-9-7

    preface In project development, annoying nulls will be encountered in both the foreground and background. If the fields in the database table allow null values, the corresponding field type in the code entity class is nullable < >, such as int?, DateTime?, The values returned from the serialization of null value fields are null. The […]

  • Cache practice

    Time:2021-9-6

    Cache update method Many R & D students use cache in this way: when querying data, first query in the cache. If the cache hits, the data will be returned directly. If it doesn’t hit, query in the database, write the data into the cache after getting the query results, and then return. When updating […]

  • PHP filters null values in arrays

    Time:2021-8-5

    array_ The filter () function filters the values in the array according to the callback function. If the callback function is omitted, the null value is filtered by default. Syntax: array_filter( array[, function] )example: $array = [ ‘IMIS project’, ”, ‘July 6, 2021’, ”, ”, ‘filter null values’ ]; //Output filtering results print_r(array_filter($array)); Array( ‘IMIS […]

  • Why is it not recommended to use equals to judge whether objects are equal?

    Time:2021-7-31

    ​ In this article, we will summarize the difference from A. equals (b), and then make a small analysis of the source code. 1、 When the value is null: 1.a.equals(b), a is null, and a nullpointexception exception is thrown. 2.a.equals(b), a is not null, B is null, and false is returned 3.Objects.equals(a, b)During comparison, if […]

  • How to realize compatibility with Oracle database in a microservice system

    Time:2021-7-31

    1、 Background Many times, our system often uses MySQL database, but suddenly we need to use Oracle database. At this time, we should consider making the system compatible with a variety of databases. 2、 Steps 1. Configure the corresponding data source in the configuration file or the service configuration file corresponding to the configuration center. […]

  • How to handle null values in SQL

    Time:2021-7-24

    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; Do you want to accurately find the MySQL articles you want to read? Here →   MySQL column directory | click here When querying […]

  • Full join null padding

    Time:2021-4-18

    Full join null padding SELECT coalesce( NULL , 0) as tianchong FROM DUAL SELECT coalesce( ” , ‘0’) as tianchong FROM DUAL   SELECT A.M, coalesce(B.N, ‘X’) AS N FROM (SELECT 0 AS M FROM DUAL UNION SELECT 1 AS M FROM DUAL UNION SELECT 2 AS M FROM DUAL UNION SELECT 3 AS M […]

  • Oracle sort one — null value processing

    Time:2021-4-12

    In daily query operation, we may need all the null values in a field to be ranked first or last. Null values can be ranked last in ascending order or first in descending order. For example, when the Mgr field in the EMP table has a null value and order by is implemented through nulls […]

  • The cache architecture is not good enough, and the system is easily paralyzed

    Time:2021-4-8

    Soul torture Caching can greatly improve the system performance and the probability of system paralysis How to prevent the cache system from being penetrated? Can cache avalanche be completely avoided? In previous articles, we introduced the advantages of cache and the problem of data consistency. In a high concurrency system, cache has become the first […]

  • These new features of es2020 are expected

    Time:2021-4-7

    Please indicate the source of Reprint: the official website of grape City, which provides professional development tools, solutions and services for developers, enabling developers. Source of the original text: https://blog.bitsrc.io/es2020-has-been-finalized-here-is-what-im-excited-about-414959bc2f7f   In recent years, with the continuous and rapid development of JavaScript and front-end field, especially after the release of ES6 in 2015, the development […]