fundamentals of database systems

---restore content starts---Database additions and deletions this is the largest database in theInster Delete Update SelectCreate and delete tables in the database (CREATE table and drop table)Commonly used keywords are where, order by, group by, and Having,limitThe CREATE table if not EXISTS table name (Field name 1 field type 1, Field Name 2 field type 2, ...);

Concurrency control is required to ensure data isolation and consistency because of the damage to the acid characteristics caused by the concurrency control of multiple transactions on the database. Problems caused by multiple transaction concurrency 1. Loss of modification (Lost update,read uncommited) T1 T2 R (a) =16 R (a) =16 W (a) =a-1 W (A) =a-1 T1 modification is lost. 2. Non-repeatable read (non-repeatable read) 2.1t1 read the data, T2 m

two numbers, the small exchange to the front, each rotation section speed after the maximum number exchange to the lastUsing a double loop to achieve bubble sortingFor example:5(n) digits are stored in a one-dimensional array, how to sortAnalysis: How many rounds the outer loop control compares, the cyclic variable iThe inner loop controls how many times each round is compared, and the loop variable JObserve the law, analyze the relationship between I and J , and finally come to a conclusionI=n

(); What if you need to enter integer data? You just need a plastic transform. int Age=int. Parse (Console.ReadLine ()); Int. The Parse () method is the function of converting a string to an integer. The specific contents of the annotation specification are as follows: 1, the class name should be used before the document comments, explain the simple function of the class and how to use. 2, the method should use comments, explain the function of the method, the meaning of the parameters, return

Properties from the popup shortcut menu. 2.in the"Database Properties"Window left"Select Page"selected in the following area"Options"object, and then the right area of the"Other Options"list, find"Status"Item, click"Restrict Access"text box, in its drop-down list, select"Single_user". 3. Click OK " " After the database name is added, the display " single user " Right-click the

Label:I. Overview1. Concept of transactionsIn a database, a transaction is a series of actions performed by a set of logical units of work, either executed or not executed. 2. Transaction acid characteristicsAtomicity (Atomic) atomicity means that multiple database operations that make up a transaction are an indivisible atomic unit, and the operations in the transaction either occur or do not occur. The co

set of properties. + Properties can be saved in a stream or loaded from a stream. - each key and its corresponding value in the property list is a string. */ + AProperties properties=NewProperties ();//instantiating an object at - //loading through the class loader - Try { -Properties.load (TestProperties2.class. getClassLoader (). getResourceAsStream ("Jdbc.properties")); - //getClassLoader () returns the class loader for this class. -

of the Oracle database is not very well understood. The above statement has a sense of déjà vu (definitely not the first love feeling), in the DB do not operate the principle of chaos. First of all, add the basics of Oracle database first.Information: (Many online)Oracle User/Table Space/table Relationship http://www.cnblogs.com/adforce/p/3312252.htmlEXPDP Tools: http://jingyan.baidu.com/article/9113f81b20

Label:When it comes to the fundamentals of database storage technology, it is necessary to understand the data characteristics and bottlenecks faced by enterprise applications. 1. Data characteristics of enterprise applications Event Generation Data As an example of courier tracking, the information read process includes the location of the current read operation, the timestamp, the current

-platform, highest performance, highest security certification. Version of Qracle: 1.8i (i:internet) 2.9i 3.10g (G:grid) 4.11g 5.12C (C:cloud) Files in the Oracle root directory: db_1: Software that primarily hosts Oracle systems, including executables, network configuration files Admin: Main store trace files generated during database running Bdump: Eligibility Sub-directory DB for saving background proces

. Updating data in a tablemysql-> UPDATE table name SET field name 1= ' A ', field name 2= ' B ' WHERE field name 3= ' C ';.12. To load data into a data table in text modemysql> LOAD DATA LOCAL INFILE "d:/mysql.txt" into table name;.13. Import. sql File commandmysql> use database name;.Mysql> SOURCE d:/mysql.sql;.14. command line to modify root passwordmysql> UPDATE mysql.user SET password=password (' New password ') WHERE user= ' root ';.mysql> FLUSH

cannot have duplicate properties. the first paradigm is a column with no duplicates. second normal form (2NF): the second paradigm is established on the basis of the first paradigm, that is, satisfying the second paradigm must first satisfy the first paradigm. The second paradigm requires that each instance or row in a database table must be divided by a unique region. It is often necessary to add a column to the table to store the unique

in this number. "K%" matches a string that begins with K.Select * from Student where FNAme like '%n% '* * NULL in the database is ' not known ' and is not interpreted in C #. There is no value.Grouping of dataThe number of people at all ages is grouped according to age:Select Fage, Count (*) from StudentGROUP BY Fage* * the GROUP BY clause must be placed after the where statement.* * the column in the GROUP BY clause does not appear in the list of co

permissions Because app users have very low privileges, they can only connect, and permissions are configured in the property configuration of the corresponding database Iv. Description of the error 1. If the Enforce password policy is checked in the General tab of Step 3, a 15128 error will occurAt this point, you need to log on as Windows Authentication mode and execute the following statement [SQL]View Plaincopy AlTER LOGIN testUser wit

t_users MODIFY uname NOT NULL means that the uname field in the T_users table is set to non-empty.2. PRIMARY KEY constraintsTo ensure uniqueness of the data in a table, there can be only one primary key in a table, but the primary key may consist of multiple fields (federated primary key, composite primary key), but this is not recommended.You can set the key in the key option when you are building a table: primary key; For example, setting the name as the primary key can be written like this:

Users'(name,fullname,password) VALUES (%s,%s,%s) ' cur.execute (sql, ("aaaaa","asd666" ,"6666"))#获取插入的最后一条数据的自增ID Print (CUR.LASTROWID) #只对一次增加一个可以直接看出, for adding multiple quantities at a time execute multiple SQL at one time='INSERT into Users (Name,fullname,password) VALUES (%s,%s,%s)'Cur.executemany (sql,[("aaadsaaa","Asd6dasd66","6666"),("adsaaaaa","asd6awf66","6666"),("awaaaaa","asd666","6666")]) Note that execute and Executemany will return the number of execution impact bars after exec

Objects Table View Stored Procedures Trigger Constraints: PRIMARY KEY constraint, FOREIGN KEY constraint, non-null constraint, UNIQUE constraint, check constraint 2.4 Database Integrity Entity integrity: The primary key field cannot be empty; Regional integrity: All data within the scope of validity; Referential integrity: Data correctness in interrelated tables, with foreign key constraints can be guara

function, aggregate function, analytic function)6.1 Single-line function6.1.1 character functions6.1.2 Date functionSysdate-System Current dateExample: select Sysdate from dual;--->dual: Virtual table6.1.3 Numeric functions6.1.4 conversion function6.1.1.1 To_char ()Convert to String typeExample: SELECT to_char (sysdate, ' YYYY ' year "fmmm" month "FMDD" Day "HH24:MI:SS") from dual;--Output system Current date6.1.1.2 to_date ()Convert to date typeExample: SELECT to_date (' 2012-01-12 ', ' YYYY-M

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,

a query statement that is treated as a result set is called a subquery, as with a normal table. SELECT * FROM (SELECT * from Student where age>20) As name Select Rom_number () over (order by age DESC) as Romnum Name,age,chinese,math from Student This stage of the database read, and I also mastered a lot of database query, build table, update, delete and other statements, the following should be the stud