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Python and SQL

SQLite SQLite is a simple relational database system, which saves its data in regular data files or even in the internal memory of the computer, i.e. It was developped for embedded applications, like Mozilla-Firefox (Bookmarks), Symbian OS or Android. SQLITE is 'quite' fast, even though it uses a simple file. Mozilla Firefox and Mozilla Thunderbird store a variety of configuration data (bookmarks, cookies, contacts etc.) in internally managed SQLite databases. Until Firefox version 57 ('Firefox Quantum'), there was a third-party add-on that used the code supporting this functionality to provide a user interface for managing arbitrary SQLite databases. Oct 15, 2020 Download SQLite Manager for Firefox. Manage, edit, manipulate, plot and save one or multiple SQLite databases simultaneously. Ess motherboards driver download for windows. Digital network & wireless cards driver download. If you're not sure where your most recent Zotero data is located, look for versions of zotero.sqlite or zotero.sqlite.bak larger than 5 MB with appropriate modification times stored elsewhere on your computer and look at the dates of the folders within the 'storage' folder.

Introduction

The history of SQL goes back to the early 70th. SQL is a Structured Query Language, which is based on a relational model, as it was described in Edgar F. Codds's 1970 paper 'A Relational Model of Data for Large Shared Data Banks. SQL is often pronounced like 'sequel'.SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987.As most people coming to this website are already familiar with mSQL, PostgresSQL, MySQL orother variants of SQL, we will not enlarge on SQL itself.
A database is an organized collection of data. The data are typically organized to model aspects of reality in a way that supports processes requiring this information.The term 'database' can both refer to the data themselves or to the database management system. The Database management system is a software application for the interaction between users database itself. Users don'thave to be human users. They can be other programs and applications as well.We will learn how Python or better a Python program can interact as a user ofan SQL database.
This is an introduction into using SQLite and MySQL from Python. The Python standard for database interfaces is the Python DB-API, which is used by Python's database interfaces.The DB-API has been defined as a common interface, which can be used to access relational databases. In other words, the code in Python for communicating with a database should be the same, regardless of the database and the database module used. Even though we use lots of SQL examples, this is not an introduction into SQL but a tutorial on the Python interface. To learn SQL you haveto consult a SQL tutorial.

SQLite

SQLite is a simple relational database system, which saves its data in regular data filesor even in the internal memory of the computer, i.e. the RAM. It was developped for embedded applications, like Mozilla-Firefox (Bookmarks), Symbian OS or Android. SQLITE is 'quite' fast,even though it uses a simple file. It can be used for large databases as well. If you want to use SQLite, you have to import the module sqlite3. To use a database, you have to create first a Connection object. The connection object will represent the database. The argument of connection - inthe following example 'companys.db' - functions both as the name of the file, where the data will be stored, and as the name ofthe database. If a file with this name exists, it will be opened. It has to be a SQLite databasefile of course! In the following example, we will open a database called company. The file does not have to exist.:

Sqlite Firefox Extension

We have now created a database with the name 'company'. It's like having sent thecommand 'CREATE DATABASE company;' to a SQL server. If you call 'sqlite3.connect('company.db')'again, it will open the previously created database.
After having created an empty database, you will most probably add one or more tables to thisdatabase. The SQL syntax for creating a table 'employee' in the database 'company' looks like this:This is the way, somebody might do it on a SQL command shell. Of course, we want todo this directly from Python. To be capable to send a command to 'SQL', or SQLite, weneed a cursor object. Usually, a cursor in SQL and databases is a control structure totraverse over the records in a database. So it's used for the fetching of the results.In SQLite (and other Python DB interfaces)it is more generally used. It's used for performingall SQL commands.
We get the cursor object by calling the cursor() method of connection. An arbitrary number of cursors can be created. The cursor is used to traverse the records from the result set. We can define a SQL command with a triple quoted string in Python:Concerning the SQL syntax: You may have noticed that the AUTOINCREMENT field is missing in the SQL code within our Python program. We have defined the staff_numberfield as 'INTEGER PRIMARY KEY' A column which is labelled like this will be automatically auto-incremented in SQLite3.To put it in other words: If a column of a table is declared to bean INTEGER PRIMARY KEY, then whenever a NULL will be used as an inputfor this column, the NULL will be automatically converted into an integer which will one larger than the highest value so far used in that column.If the table is empty, the value 1 will be used. If the largest existing value in this column has the 9223372036854775807, which is the largest possible INT in SQLite, an unused key value is chosen at random.
Now we have a database with a table but no data included. To populate the tablewe will have to send the 'INSERT' command to SQLite. We will use again theexecute method. The following example is a complete working example. To run the programyou will either have to remove the file company.db or uncomment the 'DROP TABLE' line in theSQL command:
Of course, in most cases, you will not literally insert data into a SQL table. You will rather have a lot of data inside of some Python data type e.g. a dictionary or a list, which has to be used as the input of the insert statement.
The following working example, assumes that you have already an existing database company.dband a table employee. We have a list with data of persons which will be used in the INSERT statement:
The time has come now to finally query our employee table:
If we run this program, saved as 'sql_company_query.py', we get the following result, depending on the actual data:

Sqlite Firefox Extension

MySQL

If you work under a Python 2.x version, the module MySQLdb can be used. It has to be installed. This can be accomplished under Debian or Ubuntu like this:If you work with Python 3, you have to make sure that you write everything lowercase:Of course, you have also the possibility to install it via 'pip install' inside a virtualenv:

• import the MySQLdb modul
• Open a connection to the SQL server
• Sending and receiving commands
• Closing the connection to SQL

Importing and connecting looks like this:For the following examples, we assume that you have created a user 'pytester'. You can do this e.g. on the command line with the following commands:First we start a mysql session with:On the mysql shell we continue with: Let's check the MySQL server version by using the previously created connection. To do this, we have to create a cursor object first:The output may look like this:Like in our example for sqlite3 in the beginning of this chapter, we will create a table employee and fill it with some data. The program works only under Python 3:This program returns the following output which corresponds to the insertions into the table 'employee':After this, we want to query our database again:It generates the following output: