if not null

second, the database operation 1, show databases; List databases2. Use database_name//using database_name database3. Create database Data_name//Creating a db named Data_name4. Drop database Data_name//delete a db named Data_nameThird, table

Create a data tableBefore we create a data table, let's look at the data types.1. Integral typeTINYINT 1 bytesSMALLINT 2 bytesMediumint 3 bytesINT 4 bytesBIGINT 8 bytes2. Decimal (floating point type)float[(M,d]double[(M,D)]where m represents the

1. Numeric class data column type Data column type Storage space Description Range of values TINYINT 1 bytes A very small integer Signed Value: -128~127Unsigned value: 0

[] and [[]] can determine whether the variable is empty, [ $a] [[$a]] [ ! $a] [[! $a]] No differenceIn Linux, we can use the test command to determine if a string is empty, and the test command gives us the "-Z option" and the "-N option," which you

#!/bin/bash # # Method 1a=1234;echo "$a" | [-N ' ' sed-n '/^[0-9][0-9]*$/p ' "] && echo string A is numbers the first-n is the shell's test flag on the back of the string" ' Sed-n '/^[0-9][0-9]*$/p "" To test, if not NULL, the result is true. SED

Original URL: http://www.cnblogs.com/chenssy/p/3521565.htmlHashMap is also the implementation of a hash table-based MAP interface that we use very much collection, which exists in the form of Key-value. In HashMap, Key-value is always treated as a

The so-called shared memory is the fastest available IPC form that allows multiple processes to access the same piece of memory space. is designed for inefficient operation of other communication mechanisms. It is often used in conjunction with

The same points in groovy and Java are:6+, 4+, 8+, 12+, 13, 14, 15, +, 20+, 21, 22, 23, 28+, 29+,, and 31+, 32+ + means groovy not only covers the syntax of Java, but it also has an enhanced section. The different points of groovy and Java are:0, 1,

Public classConverthelperwhereT:New() { /// ///take advantage of reflection and generics/// /// /// Public StaticListconverttolist (DataTable dt) {//Defining Collectionslist ts =NewList(); //get the

"Linux kernel design and implementation" Chapter 3 reading notesProcess management is the heart of all operating systems.First, the process1. A process is a general term for the procedure in which it is implemented and the resources it contains.2. A

Chapter III Process ManagementProcesses are the most basic of the Unix operating system abstraction concepts. Process management is the heart of all operating systems.First, the process1. The process is a procedure at the time of implementation. In

This article mainly introduces the "shell judge string is a number", mainly related to the shell to determine whether the string is a number of content, for the shell to determine whether the number of figures interested students can refer to. ?

In the 23 design modes of GOF, the singleton mode is a relatively simple one. However, sometimes the simpler things become more prone to problems. The following is a detailed discussion of the single-instance design pattern. The so-called singleton

Objective Redis linked lists are often used for Message Queuing services to complete message exchange between multiple programs. Personally, the benefit of Redis Message Queuing is that it can be distributed and shared, just like the memcache cache

var textfieldname = new Ext.form.TextField ({ ID: "Textfieldname", allowblank:false,//default is True, if it is false, NULL is not allowed If not NULL, the default hint message for the definition of the hint message is: the This field is

Reprinted from: Http://devbean.blog.51cto.com/448512/203501/in the 23 design modes of GOF, Singleton mode is a relatively simple one. However, sometimes the simpler things become more prone to problems. The following is a detailed discussion of the

3.1. Initialize the CheckerboardIn the Main.js file, we create the Newgame () method to start a new game. To start a new game, you need to do two things, one is to initialize the checker, and one is to generate two numbers in a random two grid.$

Original source: http://devbean.blog.51cto.com/448512/203501In the 23 design modes of GOF, the singleton mode is a relatively simple one. However, sometimes the simpler things become more prone to problems. The following is a detailed discussion of

Basic conceptsThe Pthread_cancel call does not wait for the thread to terminate, it only requests. The thread will continue to run after the cancellation request (PTHREAD_CANCEL) is issued.Until a cancellation point (Cancellationpoint) is reached. A

Introduction: In C # 2.0, nullable types are also introduced, nullable types are value types, but nullable types are value types that include NULL, and the following is a description of what the support for nullable types is in the next c#2.0 (I've