![]() Names must start with an ASCII letter (A-Z) or (a-z) These naming rules apply to variable and constant names, but also apply to the name of everything in Xojo including methods, modules and classes which you will learn about later. The term “variable” is used because the value that it contains can be changed by your program, so its value can vary.Ī Constant is similar to a variable, except that once its value is set it cannot be changed by your program (so it is constantly the same). Variables are great for holding information such as counter values, field values and anything else you need while your program is running. You use a concept called Variables to store information in the program's temporary memory. When you are writing code, you often need to remember things. You save things to permanent memory using files, which are discussed in the File Management section. This type of memory is also called the storage and usually a hard disk, solid-state disk (SSD) or flash memory. Permanent memory is remembered even after a computer is turned off. This is often referred to as RAM (Random Access Memory). As soon as the computer is turned off (or restarted), anything in temporary memory is lost. Temporary memory is used to remember things for as long as the computer is on. Reporting bugs and making feature requestsĪ computer has two types of memory: temporary and permanent.Starting a transaction varies depending on the database you are using. Lastly, using transactions can improve performance when adding or changing data in the database as the commit operation can be time consuming so if you do it less often (by only committing data that has been added in large chunks) you can improve performance. This prevents people from seeing data before it is ready. Second, for databases that can have multiple users, changes made in a transaction are not usually visible to other users until the transaction is marked as completed (by committing). A failure allows you to revert everything back to its initial state, sort of like an Undo. If an error occurs partway through some changes to several tables, you do not want the data to be missing in some tables. First, it ensures that data integrity is always maintained. When you are using a transaction, changes made to a database are not made permanent until you commit. This is a block of processing that either all completes successfully or none completes successfully. To learn more about general SQL, visit the W3Schools SQL Tutorial.Ĭhanges to a database are made in what is called a transaction. This is optional with some databases, but a semi-colon will be used in code samples for consistency. When you write SQL, as you will see below, it often ends in a semi-colon ( ) character which indicates the "end of the SQL command". This section shows some example of generic SQL that ought to work across most databases. ![]() ![]() These commands are: SELECT, INSERT, UPDATE, DELETE, COMMIT and ROLLBACK. Regardless, there are several common SQL commands that are always available, even if their specific syntax changes slightly depending on the database you are using. This can make it challenging to switch between database engines (such as SQLite and PostgreSQL, for example) because the SQL used to send commands to the database may be different. But as you create more complex SQL, you'll find that each database has their own slightly different variant of SQL. For simple SQL commands, SQL is often the same across different databases. SQL is the way to send commands to the database to do things such as create tables or get data from tables. The collection of your tables is called the "database schema" or "database design".ĭatabase engines all share a similar command structure, which is called SQL, which stands for Structured Query Language and is often pronounced as "sequel". You can look up the teams for the other players using the same technique. So both Bob and Tom are on the Seagulls team. Looking in the Team table from above, you can see that the team with ID = 1 is the Seagulls. For example, you can see that Bob and Tom both have TeamID = 1. It clearly tells you the team to which the player belongs. This column defines the relationship between Player and Team. But in addition, it also has a TeamID column. Notice that the Player table has its own ID column as well. Here is an example of a Player table with sample data: For example, to track the players for each team you would have another table, called Player, that is related to the Team table. And these tables are often related in some way, which is why these are called relational databases. Reporting bugs and making feature requestsĪ database usually consists of many tables.Considerations when using a database with a web application.
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