relational database normalization

Relational database,1. Create a table 1 create table student (2 sno char (8), 3 sname char (8), 4 sbirth date, 5 ssex char (2), 6 sdept char (30) 7 ); 2. delete a table 1 drop table student1; 3. Common Data Types 4. Declare the primary code 1 create table student (2 sno char (8) primary key, 3 sname char (8), 4 sbirth date, 5 ssex char (2), 6 sdept char (30) 7 ); 5. Declare external code 1 cre

(Original) based on the tree structure data stored in the chain of the relational database system, calculate the algorithm of all the nodes of the subtree under a node (t-SQL language implementation) Create Function f_subtree (@ dpcode varchar (9)/* tree structure data, which is used to find the User-Defined Function of all the nodes of the subtree under a node */Returns @ new table ([dpcode] [varchar] (9),

This week is reviewing the "Introduction to Database System" This course, see this section of relational operations, for the addition of operations is not very understanding. Through Baidu, I do not feel that it is easier to understand the explanation. Here, I would like to share my understanding, if there is a mistake in the place, but also want to see this blog to give you guidance. First of all, I h

number, manufacturer's name, component number, and manufacturer's address, but also manufacturer's name, the manufacturer's address, so there is a non-primary attribute transfer dependency on the main attribute, which does not conform to the third normal form requirementAfter modification:BC Paradigm: Based on the first paradigm, each non-trivial dependency must have a key code on the left side, and each determinant must contain a key code. Wikis: Any property, including non-primary and primary

Tags: type brackets unique order Chinese word breaker query files multiple columnsImprove query speed, facilitate sorting and grouping. (The process of sorting and grouping, if not indexed, results in temporary tables and filesort)Based on business logic, analyze the frequency and order of column queries, and build indexes and composite indexes.Primary key index (primary key),----> No index name is required because there is only one primary key indexUnique index (single key)---->unique Key Email

Label:Count: Count rows Select COUNT (*) from student Select count (age) from student/* will not count null values */ Sum: Returns the sum of the values in the column and automatically skips the null value (numeric +null=null) Select SUM (age) from student Avg: Returns the average of all values in the result set Select AVG (age) from student Max/min: Returns the maximum/small value in all values Select Max (age) from student GROUP BY: Data Group query Select Age,name,count (*) from the student

 1. Master-slave replication is MongoDB The most commonly used replication method, which is very flexible and can be used for backup, failure recovery, read extension, etc.2 The most basic way to set up is to establish a master node and one or more slave nodes, each from the node to know the address of the master node. The primary server is started by running Mongod–master. Running mongod–slave–source master_address initiates the slave server, where master_address is the address of the prima

Tags: type SQL statement Delete Insert Number unique index explain not slow query1, positioning slow query-find out the execution slow SQL.2, suitable table structure, appropriate engine, index, partition table, SQL optimization (single machine Optimization).3, Multi-machine optimization--read/write separation (cluster), distributed.4, the cache scheme.Parsing slow query: Explain + SQL statement "using MySQL client"Indexes are at the expense of insertion, modification, and deletion (because addi

Label:MongoDB Grammar MySQL syntax Db.test.find ({' name ': ' Foobar '}) Db.test.find () Db.test.find ({' ID ': ten}). Count () Db.test.find (). Skip () Limit Db.test.find ({' ID ': {$in: [25,35,45]}} Db.test.find (). Sort ({' ID ': -1}) Db.test.distinct (' name ', {' ID ': {$lt:}}) Db.test.group ({key:{' name ': ' true},cond:{' name ': ' foo '},reduce:function (obj,prev) {prev.msum+=obj.marks;},initial: {msum:0}}) Db.test.find (' this.id Db.test.insert ({' name ': ' Foobar ', ' age '

Tags: relational database Database system query optimization relationshipQuery optimizationHas a very important position in the relational database system.Relational query optimization is a key factor affecting RDBMS performanceBecause the semantic level of the