data warehousing fundamentals

(18): Suitable for fixed-length charactersEg: identity card (18), when fixed in length, the char type is more efficient than the varchar typevarchar (): type that is suitable for characters that cannot be fixed lengthNote: The default length of no write length is 1Text: Long text informationNchar,nvarchar,ntext:N:unicode: Supports double-byte encoding. (Kanji, Korean ...)This double-byte text with n is more suitable for storing Chinese characters.Bit: (bit) 0 or 1 (usually when BOOL is used)Eg:

parameter append is True, indicating append, and false to no appendThe code is as follows:1 PackageCom.himi.fileoutputstream;2 3 ImportJava.io.FileOutputStream;4 Importjava.io.IOException;5 6 7 /**8 * How to implement data append write? 9 * Using construction Method: FileOutputStream (String name, Boolean append)Ten * The parameter append is True, indicating append, and false to not append One */ A - - Public classFileOutputStreamDemo5 { the -

return a DataReader object that can read multiple records from the database by DataReader.DataReader ObjectAdo. NET DataReader objects can retrieve read-only, forward-only streams of data from the data source, extracting only one record from the data source at a time. Using DataReader can improve the performance of your application and reduce system overhead. Da

[] args)throwsIOException { - //Encapsulating Data Sources -BufferedReader br =NewBufferedReader (NewFileReader ("B.txt")); - // Encapsulate Destination (Create collection Object) -arraylistNewArraylist(); - in //read data stored in the collection -String line =NULL; to while(line = Br.readline ())! =NULL) { + Array.add (line); - } the * //Freeing Resources

the result of knowing the meaning of the name5. Assignment Operator: = Assign the right value to the left6. Arithmetic operators: +-*/(except)% (take surplus)7. num++; num=num+1; Num+=1;num--; Num=num-1; Num-=1;System.out.println (--num);//calculate and re-output firstSystem.out.println (num--);//First output recalculation8.double avg= (90+99)/3.0 automatic type conversion occursAutomatic conversion type conditions:1) Type-compatible: (int and double are numeric)2) The target type is greater th

path, but pass a OutputStream object?A: The reason is simple, the byte buffer stream only provides buffers, designed for efficiency. However, the actual read and write operation is also dependent on the basic flow object implementation.3. Bufferedoutputstream Write Data , code example:1 Packagecn.itcast_05;2 3 ImportJava.io.BufferedOutputStream;4 ImportJava.io.FileOutputStream;5 Importjava.io.IOException;6 7 Public classBufferedoutputstreamdemo {8

Introduction: Title ImportJava.io.FileInputStream;/** * @authorCzchina **/ Public classTeststream { Public Static voidMain (string[] args) {//TODO auto-generated Method Stub//declaring a reference to an input streamFileInputStream FLS =NULL; //declaring a reference to the output streamFileOutputStream fos =NULL; Try{ //first, generate an object representing the input streamFLS =NewFileInputStream ("E:/android/androidstudioprojects/text.txt"); //generating a byte array byte[

= new float (F1);Double D1 = F1.doublevalue ();e.g: double--->intDouble D1 = 100.00;Double D1 = new double (d1);int i1 = D1.intvalue ();(6) Conversion of string types to other data typesClass Test {public static void Main (String args[]) {int i1 = 10;float f1 = 3.14f;Double D1 = 3.1415926;Integer I1 = new Integer (i1);float F1 = new float (F1);Double D1 = new double (d1);String SI1 = i1.tostring ();String sf1 = F1 . toString ();String SD1 = D1. toStr

1. Create a byte output stream object and do a few things:(1) Call system function to create file(2) Create Fos object(3) Point the Fos object to this file2. code example:1 PackageCom.himi.fileoutputstream;2 3 ImportJava.io.File;4 Importjava.io.FileNotFoundException;5 ImportJava.io.FileOutputStream;6 Importjava.io.IOException;7 8 /*9 * Create file Fos.txt, write string: Hello WorldTen * One * Operation flow of the output of the byte stream: A * A: Create byte output stream object - * B: Write

1. FileInputStream reading data One byte array at a time byte[]Use FileInputStream to read one byte array at a time:int read (byte[] b)　　return value : The return value is actually the number of bytes actually read.2. code example:1 PackageCom.himi.fileinputstream;2 3 ImportJava.io.FileInputStream;4 Importjava.io.IOException;5 6 7 8 /**9 * Ten * Use FileInputStream one byte array at a time: int read (byte[] b) One * Return value: The return value is

long typeOtherwise it will be converted to int type;Converting a large range of numeric types to a small range of numeric types requires an explicit conversion and may be accompanied by a loss of precision.Examples of interview questions1. (false?) 10.9:9) What is the value?Java is automatically type-converted based on the precision type of the operator, and 9 is automatically converted to 9.0 due to the presence of 10.9. So the result is 9.0.2. Char x= "9"; (false?) X:10) The value of why?When

: Public class Test { publicstaticvoid main (String args[]) { int num =-1; System. out. println (num>>>1 );} }Output: 2147483647~: bitwise reverse;: bitwise AND;|: bitwise OR;^: Bitwise XOR;But what is the use of these things, refer to the following JS code, the original link:(! (~+[])+{})[--[~+""][+[]]*[~+[]] + ~~!+[]]+({}+[])[[~!+[]]*~+[]]Will output: "SB"Or do you like this?((""[~+[]]++)+"") [(+[])]+ (!+[]+{}) [(~ (~+[]+~+[]) Will output: "Ne"Reference to the conversion

One, servlet declaration cycleThe 1.Servlet declaration cycle is generally divided into four steps: Load, instantiate, service, destroy.2. Instantiation is performed only once throughout the life cycle.Second, JSP1.Servlet providing data to the JSPRequest.setattribute (,);Example: Request.setattribute ("Key", "Hello");2.Servlet Jump JSP(1) Same request method: Request.getrequestdispatcher ("/path"). Forward (request, response);The request jump can onl

operations, using for-in, for, while, and do-while for looping. Wrapping conditions and loop variable parentheses can be omitted, but curly braces on the body of the statement are required.(6.1) for in control flowLet Indivadulscore = [70,66,80,90,56,34]var score = 0For S in Indivadulscore{If s>60{Score + = 20}else{Score + = 100}}Note: Look at the differences in the syntax of the control flow you wrote earlier(6.2)? indicates an optionalvar optionstring:string? = "Hello,world"Optionstring = = N

. NET Foundation:. NET and C #. NET is a platform C # is a languagePurpose of. NetA. Desktop Application B. Web application C. Professional game development (XBOX360) D. Embedded device software development E. Smartphone app development F. Tablet app developmentBusiness:static void Main (string [] args) Main function, method entryCompiler principle:1. Write the source code;The 2.c# compiler compiles C # source code into MSIL;3. Give the intermediate code to the CLR's instant compiler (JIT) to co

Ck:candidate itemset of size klk:frequent itemset of size kL1 = {Frequent items};for (k = 1; Lk! =?; k++) does begin Ck+1 = candidates generated from Lk; For each transaction t in database does increment the count of all candidates in ck+1 that is contained in T lk+1 = candidates in ck+1 with Min_support Endreturn? k Lk;SQL applicationSuppose the items in Lk-1 is listed in a orderstep 1:self-joining Lk-1 insert INTO Ckselect p.item1, p.item2, ..., P.item K-1, Q.itemk-1from Lk-1 p,

In recent years, many people have heard a noun "big data" also some people choose to learn to understand big data, so what is big data in the end, to learn big data need to have Java Foundation?Recommend a big Data learning Exchange Group 119599574 every night, there is a "f

data link layer, along with the hardware address of the local host or default gateway. The data link layer adds a header in front of the packet so that the data block becomes true ( it is called a frame because it adds both a header and a trailer to the grouping, making it resemble a book file ). The frame contains an Ethernet type (ether-type) field that indica

follows.DELETE from StudentsWHERE SName = ' Zhang Qing cut 'In another case, if the primary key value of the row to be deleted is referenced by another table, for example, the StudentID in the score table refers to the SCODE column in the Student information table, then the referenced row is deleted:DELETE from StudentsWHERE SCode = 22SQL Server will report error messages that conflict with constraintsTip: The DELETE statement deletes the entire record and does not delete only a single column,