Category：Other DB
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Time：2019-6-30
1. Installation Using the following command, the latest version will be installed automatically, which is 9.5 here. sudo apt-get install postgresql When the installation is completed, the default will be: (1) Create a Linux user named “postgres” (2) Create a default database account named “postgres” with no password as the database administrator (3) Create a […]
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Time：2019-6-29
What is a window function? A window function performs a calculation on a series of table rows that are somewhat related to the current row. This is comparable to the calculation performed by an aggregate function. However, window functions do not aggregate multiple rows into a single output line, which is different from the usual […]
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Time：2019-6-28
Background of the problem Many developers and testers may encounter a list of data that shows the data on the previous page when it is turned down, that is, there will be duplicate data when it is turned over. How to deal with it? The reason for this problem is that the selected sorting fields […]
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Time：2019-6-27
abstract One important aspect of relational databases is query speed. The query speed directly affects the quality of a system. Query speed generally needs to peek at the execution process through query planning. The query path chooses the path with the lowest query cost to execute. And how does this cost come out? Parameters and […]
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Time：2019-6-26
background A common design for dealing with hierarchical structures with uncertain depths, such as organizational structures, is to store IDs and arent_IDs in a table and construct a tree by self-joining. This approach is very friendly to the process of writing data, but the query process becomes relatively complex. Without introducing MPTT model, a node […]
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Time：2019-6-25
It provides multi-version parallel control, supports almost all SQL components (including subqueries, transaction and user-defined types and functions), and provides a very wide range of (development) language bindings (including C, C++, Java, perl, tcl, and python). This paper introduces its installation process under Windows system. Generally speaking, a modern Unix-compatible platform should be able to […]
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Time：2019-6-24
As far as I know, there are four domestic databases in China, three of which are based on PostgreSQL. And because of the flexibility of the license, anyone can use, modify, and distribute PostgreSQL for any purpose free of charge, whether for private, commercial or academic use. This article just briefly introduces the installation and […]
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Time：2019-6-23
There are N postgres. exes in the process (this is normal, see official documentation), but one is always full of CPU (because the machine is dual-core, occupying 50% of the resources). The pgAdmin III connection that comes with it will die. The question was not answered by an online search. Looking at the log, we […]
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Time：2019-6-22
Because of a project requirement, you need to install postgreSQL, so download the installation file of.Exe to run. It went well at first, but in the end, when the database was initialized, a damn dialog box appeared. (Draw a circle here to curse Microsoft, the error dialog box he jumped out of never helped.) Cloud: […]
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Time：2019-6-21
XML Content Generation PartFunctions that generate XML from SQL data.1. xmlcomment: Generate annotation functions. xmlcomment(text ) Example: SELECT xmlcomment(‘hello’); xmlcomment ————– <!–hello–> 2. xmlconcat: XML connection function xmlconcat(xml [, …]) Example:SELECT xmlconcat(‘<abc/>’, ‘<bar>foo</bar>’); xmlconcat ———————- <abc/><bar>foo</bar> If there are multiple version declarations in the connected XML data, only one version declaration will exist in the […]
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Time：2019-6-20
1. Use EXPLAINThe EXPLAIN command allows you to view the execution plan, as described in the previous blog. This method is our main debugging tool. 2. Update the statistical information used in the implementation plan in a timely manner Since statistical information is not updated every time the database is operated, it is usually updated […]
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Time：2019-6-19
The steps to create a table partition are as follows:1. Create the main tableCREATE TABLE users ( uid int not null primary key, name varchar(20)); 2. Create partition tables (must inherit the above table) CREATE TABLE users_0 ( check (uid >= 0 and uid< 100) ) INHERITS (users); CREATE TABLE users_1 ( check (uid >= […]
