Explain Explained in PostgreSQL - How Databases Prepare Optimal Query Plans to Execute SQL

In This video I’ll go through how Explain works in PostgreSQL, explain is the command that you add to the beginning of your SQL to return details about how the database is going to execute the statement.

#postgresql #databases

What is GEEK

Buddha Community

Explain Explained in PostgreSQL - How Databases Prepare Optimal Query Plans to Execute SQL
Cayla  Erdman

Cayla Erdman

1594369800

Introduction to Structured Query Language SQL pdf

SQL stands for Structured Query Language. SQL is a scripting language expected to store, control, and inquiry information put away in social databases. The main manifestation of SQL showed up in 1974, when a gathering in IBM built up the principal model of a social database. The primary business social database was discharged by Relational Software later turning out to be Oracle.

Models for SQL exist. In any case, the SQL that can be utilized on every last one of the major RDBMS today is in various flavors. This is because of two reasons:

1. The SQL order standard is genuinely intricate, and it isn’t handy to actualize the whole standard.

2. Every database seller needs an approach to separate its item from others.

Right now, contrasts are noted where fitting.

#programming books #beginning sql pdf #commands sql #download free sql full book pdf #introduction to sql pdf #introduction to sql ppt #introduction to sql #practical sql pdf #sql commands pdf with examples free download #sql commands #sql free bool download #sql guide #sql language #sql pdf #sql ppt #sql programming language #sql tutorial for beginners #sql tutorial pdf #sql #structured query language pdf #structured query language ppt #structured query language

Grace  Lesch

Grace Lesch

1639778400

PySQL Tutorial: A Database Framework for Python

PySQL 

PySQL is database framework for Python (v3.x) Language, Which is based on Python module mysql.connector, this module can help you to make your code more short and more easier. Before using this framework you must have knowledge about list, tuple, set, dictionary because all codes are designed using it. It's totally free and open source.

Tutorial Video in English (Watch Now)

IMAGE ALT TEXT HERE

Installation

Before we said that this framework is based on mysql.connector so you have to install mysql.connector first on your system. Then you can import pysql and enjoy coding!

python -m pip install mysql-connector-python

After Install mysql.connector successfully create Python file download/install pysql on the same dir where you want to create program. You can clone is using git or npm command, and you can also downlaod manually from repository site.

PyPi Command

Go to https://pypi.org/project/pysql-framework/ or use command

pip install pysql-framework

Git Command

git clone https://github.com/rohit-chouhan/pysql

Npm Command

Go to https://www.npmjs.com/package/pysql or use command

$ npm i pysql

Snippet Extention for VS Code

Install From Here https://marketplace.visualstudio.com/items?itemName=rohit-chouhan.pysql

IMAGE ALT TEXT HERE

Table of contents

Connecting a Server


To connect a database with localhost server or phpmyadmin, use connect method to establish your python with database server.

import pysql

db = pysql.connect(
    "host",
    "username",
    "password"
 )

Create a Database in Server


Creating database in server, to use this method

import pysql

db = pysql.connect(
    "host",
    "username",
    "password"
 )
 pysql.createDb(db,"demo")
 #execute: CREATE DATABASE demo

Drop Database


To drop database use this method .

Syntex Code -

pysql.dropDb([connect_obj,"table_name"])

Example Code -

pysql.dropDb([db,"demo"])
#execute:DROP DATABASE demo

Connecting a Database


To connect a database with localhost server or phpmyadmin, use connect method to establish your python with database server.

import pysql

db = pysql.connect(
    "host",
    "username",
    "password",
    "database"
 )

Creating Table in Database


To create table in database use this method to pass column name as key and data type as value.

Syntex Code -


pysql.createTable([db,"table_name_to_create"],{
    "column_name":"data_type", 
    "column_name":"data_type"
})

Example Code -


pysql.createTable([db,"details"],{
    "id":"int(11) primary", 
     "name":"text", 
    "email":"varchar(50)",
    "address":"varchar(500)"
})

2nd Example Code -

Use can use any Constraint with Data Value


pysql.createTable([db,"details"],{
    "id":"int NOT NULL PRIMARY KEY", 
     "name":"varchar(20) NOT NULL", 
    "email":"varchar(50)",
    "address":"varchar(500)"
})

Drop Table in Database


To drop table in database use this method .

Syntex Code -

pysql.dropTable([connect_obj,"table_name"])

Example Code -

pysql.dropTable([db,"users"])
#execute:DROP TABLE users

Selecting data from Table


For Select data from table, you have to mention the connector object with table name. pass column names in set.

Syntex For All Data (*)-

records = pysql.selectAll([db,"table_name"])
for x in records:
  print(x)

Example - -

records = pysql.selectAll([db,"details"])
for x in records:
  print(x)
#execute: SELECT * FROM details

Syntex For Specific Column-

records = pysql.select([db,"table_name"],{"column","column"})
for x in records:
  print(x)

Example - -

records = pysql.select([db,"details"],{"name","email"})
for x in records:
  print(x)
#execute: SELECT name, email FROM details

Syntex Where and Where Not-

#For Where Column=Data
records = pysql.selectWhere([db,"table_name"],{"column","column"},("column","data"))

#For Where Not Column=Data (use ! with column)
records = pysql.selectWhere([db,"table_name"],{"column","column"},("column!","data"))
for x in records:
  print(x)

Example - -

records = pysql.selectWhere([db,"details"],{"name","email"},("county","india"))
for x in records:
  print(x)
#execute: SELECT name, email FROM details WHERE country='india'

Add New Column to Table


To add column in table, use this method to pass column name as key and data type as value. Note: you can only add one column only one call

Syntex Code -


pysql.addColumn([db,"table_name"],{
    "column_name":"data_type"
})

Example Code -


pysql.addColumn([db,"details"],{
    "email":"varchar(50)"
})
#execute: ALTER TABLE details ADD email varchar(50);

Modify Column to Table


To modify data type of column table, use this method to pass column name as key and data type as value.

Syntex Code -

pysql.modifyColumn([db,"table_name"],{
    "column_name":"new_data_type"
})

Example Code -

pysql.modifyColumn([db,"details"],{
    "email":"text"
})
#execute: ALTER TABLE details MODIFY COLUMN email text;

Drop Column from Table


Note: you can only add one column only one call

Syntex Code -

pysql.dropColumn([db,"table_name"],"column_name")

Example Code -

pysql.dropColumn([db,"details"],"name")
#execute: ALTER TABLE details DROP COLUMN name

Manual Execute Query


To execute manual SQL Query to use this method.

Syntex Code -

pysql.query(connector_object,your_query)

Example Code -

pysql.query(db,"INSERT INTO users (name) VALUES ('Rohit')")

Inserting data


For Inserting data in database, you have to mention the connector object with table name, and data as sets.

Syntex -

data =     {
    "db_column":"Data for Insert",
    "db_column":"Data for Insert"
}
pysql.insert([db,"table_name"],data)

Example Code -

data =     {
    "name":"Komal Sharma",
    "contry":"India"
}
pysql.insert([db,"users"],data)

Updating data


For Update data in database, you have to mention the connector object with table name, and data as tuple.

Syntex For Updating All Data-

data = ("column","data to update")
pysql.updateAll([db,"users"],data)

Example - -

data = ("name","Rohit")
pysql.updateAll([db,"users"],data)
#execute: UPDATE users SET name='Rohit'

Syntex For Updating Data (Where and Where Not)-

data = ("column","data to update")
#For Where Column=Data
where = ("column","data")

#For Where Not Column=Data (use ! with column)
where = ("column!","data")
pysql.update([db,"users"],data,where)

Example -

data = ("name","Rohit")
where = ("id",1)
pysql.update([db,"users"],data,where)
#execute: UPDATE users SET name='Rohit' WHERE id=1

Deleting data


For Delete data in database, you have to mention the connector object with table name.

Syntex For Delete All Data-

pysql.deleteAll([db,"table_name"])

Example - -

pysql.deleteAll([db,"users"])
#execute: DELETE FROM users

Syntex For Deleting Data (Where and Where Not)-

where = ("column","data")

pysql.delete([db,"table_name"],where)

Example -

#For Where Column=Data
where = ("id",1)

#For Where Not Column=Data (use ! with column)
where = ("id!",1)
pysql.delete([db,"users"],where)
#execute: DELETE FROM users WHERE id=1

--- Finish ---

Change Logs

[19/06/2021]
 - ConnectSever() removed and merged to Connect()
 - deleteAll() [Fixed]
 - dropTable() [Added]
 - dropDb() [Added]
 
[20/06/2021]
 - Where Not Docs [Added]

The module is designed by Rohit Chouhan, contact us for any bug report, feature or business inquiry.

Author: rohit-chouhan
Source Code: https://github.com/rohit-chouhan/pysql
License: Apache-2.0 License

#python 

Ruth  Nabimanya

Ruth Nabimanya

1621850444

List of Available Database for Current User In SQL Server

Introduction

When working in the SQL Server, we may have to check some other databases other than the current one which we are working. In that scenario we may not be sure that does we have access to those Databases?. In this article we discuss the list of databases that are available for the current logged user in SQL Server

Get the list of database
Conclusion

#sql server #available databases for current user #check database has access #list of available database #sql #sql query #sql server database #sql tips #sql tips and tricks #tips

Ruth  Nabimanya

Ruth Nabimanya

1620633584

System Databases in SQL Server

Introduction

In SSMS, we many of may noticed System Databases under the Database Folder. But how many of us knows its purpose?. In this article lets discuss about the System Databases in SQL Server.

System Database

Fig. 1 System Databases

There are five system databases, these databases are created while installing SQL Server.

  • Master
  • Model
  • MSDB
  • Tempdb
  • Resource
Master
  • This database contains all the System level Information in SQL Server. The Information in form of Meta data.
  • Because of this master database, we are able to access the SQL Server (On premise SQL Server)
Model
  • This database is used as a template for new databases.
  • Whenever a new database is created, initially a copy of model database is what created as new database.
MSDB
  • This database is where a service called SQL Server Agent stores its data.
  • SQL server Agent is in charge of automation, which includes entities such as jobs, schedules, and alerts.
TempDB
  • The Tempdb is where SQL Server stores temporary data such as work tables, sort space, row versioning information and etc.
  • User can create their own version of temporary tables and those are stored in Tempdb.
  • But this database is destroyed and recreated every time when we restart the instance of SQL Server.
Resource
  • The resource database is a hidden, read only database that holds the definitions of all system objects.
  • When we query system object in a database, they appear to reside in the sys schema of the local database, but in actually their definitions reside in the resource db.

#sql server #master system database #model system database #msdb system database #sql server system databases #ssms #system database #system databases in sql server #tempdb system database

Introduction to Recursive CTE

This article will introduce the concept of SQL recursive. Recursive CTE is a really cool. We will see that it can often simplify our code, and avoid a cascade of SQL queries!

Why use a recursive CTE ?

The recursive queries are used to query hierarchical data. It avoids a cascade of SQL queries, you can only do one query to retrieve the hierarchical data.

What is recursive CTE ?

First, what is a CTE? A CTE (Common Table Expression) is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. For example, you can use CTE when, in a query, you will use the same subquery more than once.

A recursive CTE is one having a subquery that refers to its own name!

Recursive CTE is defined in the SQL standard.

How to make a recursive CTE?

A recursive CTE has this structure:

  • The WITH clause must begin with “WITH RECURSIVE”
  • The recursive CTE subquery has two parts, separated by “UNION [ALL]” or “UNION DISTINCT”:
  • The first part produces the initial row(s) for the CTE. This SELECT does not refer to the CTE name.
  • The second part recurses by referring to the CTE name in its FROM clause.

Practice / Example

In this example, we use hierarchical data. Each row can have zero or one parent. And it parent can also have a parent etc.

Create table test (id integer, parent_id integer);

insert into test (id, parent_id) values (1, null);

insert into test (id, parent_id) values (11, 1);
insert into test (id, parent_id) values (111, 11);

insert into test (id, parent_id) values (112, 11);

insert into test (id, parent_id) values (12, 1);

insert into test (id, parent_id) values (121, 12);

For example, the row with id 111 has as ancestors: 11 and 1.

Before knowing the recursive CTE, I was doing several queries to get all the ancestors of a row.

For example, to retrieve all the ancestors of the row with id 111.

While (has parent)

	Select id, parent_id from test where id = X

With recursive CTE, we can retrieve all ancestors of a row with only one SQL query :)

WITH RECURSIVE cte_test AS (
	SELECT id, parent_id FROM test WHERE id = 111
	UNION 
	SELECT test.id, test.parent_id FROM test JOIN cte_test ON cte_test.id = test.parent_id

) SELECT * FROM cte_test

Explanations:

  • “WITH RECURSIVE”:

It indicates we will make recursive

  • “SELECT id, parent_id FROM test WHERE id = 111”:

It is the initial query.

  • “UNION … JOIN cte_test” :

It is the recursive expression! We make a jointure with the current CTE!

Replay this example here

#sql #database #sql-server #sql-injection #writing-sql-queries #sql-beginner-tips #better-sql-querying-tips #sql-top-story