tabular database vs relational database

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: mysql spring mvc+my batis dubbo+zookeerper restful redis distributed cacheMySQL is a relational database management system developed by the Swedish MySQL AB company and is currently part of Oracle's product portfolio. MySQL is one of the most popular relational database management systems, and MySQL is the best R

A long time ago, I knew that Microsoft's Petshop was very classic. I took the time to study yesterday. At the beginning, I was not very familiar with what kind of membership is, run petshop to learn from login, but the user name and password do not know, and later found a more registered page, registered a page, only to find that you have to go from the database. It took so much time to finally return to the datab