null test

PostgreSQL solves the tinyint data type problem in a system database, creating the data types that you need:CREATE DOMAIN tinyintAs smallintCONSTRAINT tinyint_check Check (value >= 0 and value ALTER DOMAIN tinyintOWNER to Postgres;COMMENT on DOMAIN

Compile a JavaRobot-based screen capture tool-general Linux technology-Linux programming and kernel information. The following is a detailed description. Java Fun and Games (Java entertainment and Games) provides the ability to capture the home

Several examples show the mode space and the reserved space of sed.Example 1Sed g outputs a blank line under each line of the documentCode:$ Cat foo1111111111111122222222222222333333333333334444444444444455555555555555$ Sed g foo11111111111111 222222

PHP is a weak type of programming language. In a PHP program, the data type of a variable can change automatically as its value differs, and PHP does not force checks or constraints on the data type of the variable. We can refer to one of the

I used to write an article about smart pointers.ArticleBut I still haven't figured out two things: 1. How can I call a member function of an object directed by a smart pointer? I don't know how to access the member method of an object through a

Php5 type constraints learning notes. Php is a weak programming language. In a php program, the data type of a variable can automatically change with its value, php does not forcibly check the data types of variables. php is a weak programming

Php is a weak programming language. in php programs, the data types of variables can automatically change with their values, php does not forcibly check or constrain the data type of the variable. Php is a weak programming language. in php programs,

This article mainly introduces the basic learning tutorial of MySQL triggers, including the basic knowledge of trigger creation and management! For more information, see 0. basic concepts of triggersA trigger is a special stored procedure that

Ways to improve query speed with data above tens:1. Try to avoid using the! = or <> operator in the WHERE clause, or discard the engine for a full table scan using the index.2. To optimize the query, avoid full-table scanning as far as possible, and

From: http://lz12366.iteye.com/blog/673290 The concept of null value is a common cause of confusion among SQL beginners. They often think that null is the same as an empty string. No! For example, the following statements are completely different:

--Servelet: for receiving requests (client, browser), responding, server-side, Java class--Servletlogin--Java implementation of Web Project Server response PackageCom.dragon.java.servlet;Importjava.io.IOException;ImportJava.io.PrintWriter;Importjava.

Java Exception handling mechanismTop-level class for Throwable class exceptionsSub-classError: System-level errorsStack memory OverflowException: Program-level errorsCan be solved by capturing the mechanism classTry Statementtry{Code snippets that

Analysis of java Dynamic proxyRecently, the company saw the use of MapperScannerConfigurer in the integration of mybatis and spring. This class automatically generates an interface-based Dynamic proxy class through reverse proxy. So I remembered the

Java simple factory mode, java factory ModeHead First design pattern Learning Category Simple Factory) Factory Method) Abstract Factory) Introduction Simple factory mode: A simple factory is not a design pattern, but rather a programming

Self-summary, what is wrong or not in place, please point out, thank you!Objective: To master the occurrence of null values in Java and avoid nullpointerexceptionCode Environment Readiness: JUnit needs to be introduced and the code package part

In some Java projects, Mapperscannerconfigurer is used in MyBatis and spring consolidation, which automatically generates an interface based dynamic proxy class through a reverse proxy. In view of this, this article analyzes the Java dynamic Proxy.

Preface There are three patterns in the design pattern that are related to the factory pattern: The Simple factory model, the factory method pattern, and the abstract factory pattern. In the previous article has talked about the first two kinds,

Using transactions in MySQL stored procedures1 DROP PROCEDURE IF EXISTSTEST_SP12 CREATE PROCEDURETest_sp1 ()3 BEGIN 4 DECLARET_errorINTEGER DEFAULT 0; 5 DECLARE CONTINUEHANDLER forSQLEXCEPTIONSETT_error=1; 6 7STARTTRANSACTION; 8

JDBC's self-growth and transaction1. Self-growthThere is a phenomenon: there are two tables in the database (student name, Class), Class table ( class number (self-growing primary key), class number).Now I insert a message into the class table, only

I encountered a problem when I was developing a project within the company:Select student_quality_id from student_quality where Mark_status=0 and batch_stauts in (2,3)The result encountered a student_quality_id that had been unable to find a