The Expression Builder is a component of Microsoft Access that helps you build expressions. It allows you to look up and build expressions without having to remember how to type the full expression.
In database terms, a schema (pronounced “skee-muh” or “skee-mah”) is the organisation and structure of a database. Both schemas and schemata can be used as plural forms.
A schema contains schema objects, which could be tables, columns, data types, views, stored procedures, relationships, primary keys, foreign keys, etc.
A database schema can be represented in a visual diagram, which shows the database objects and their relationship with each other.
Above is a simple example of a schema diagram. It shows three tables, along with their data types, relationships between the tables, as well as their primary keys and foreign keys.
MySQL is an open source relational database management system (RDBMS). It is the world’s most popular open source RDBMS and is currently ranked as the second most popular RDBMS in the world (behind Oracle Database).
MySQL is available as a free download, however, several paid editions are also available which offer additional functionality.
As the name suggests, MySQL is based on SQL. The “My” part is named after co-founder Michael Widenius’ daughter, My.
Microsoft Access is a relational database management system (RDBMS) developed by Microsoft. It’s part of the Microsoft Office suite, included in the Professional and higher editions or sold separately.
Microsoft Access provides a quick and easy way to develop databases and is particularly well suited for individuals and small business. Access is the most popular desktop database on the market.
In Access, most tasks can be performed via the graphical user interface (GUI), but more advanced users can also develop applications using Visual Basic for Applications (VBA) code. Advanced users can also use SQL code to write or modify queries.
SQL Server is a relational database management system (RDBMS) developed by Microsoft. It is Microsoft’s enterprise level RDBMS offering, and is a more sophisticated and robust system than Access, which has traditionally been a desktop system.
SQL Server’s main competitors are Oracle Database, MySQL (now owned by Oracle), PostgreSQL, and IBM’s DB2.
SQL Server is a client-server based system, which means that it operates as a server, typically containing many databases, with multiple clients accessing the databases from across a network. These clients are often other applications (such as a website or CRM system). This is in contrast to desktop systems, where the database will often (but not necessarily) reside on the user’s computer.
SQL is the standard language for querying data inside a relational database management system (RDBMS). It is supported by all of the major database systems, such as Microsoft Access, SQL Server, MySQL, Oracle, PostgreSQL, DB2, etc.
SQL is a relatively easy language to learn when compared to most programming languages. It is based on SQL “statements” that, at times, can resemble natural language.
For example:
SELECT CustomerName FROM Customers WHERE CustomerId = 1
The above SQL statement is asking the database to:
“Select the value of the CustomerName column from the Customers table where the CustomerId column’s value equals 1“.
MySQL Workbench is a graphical tool for working with MySQL.
MySQL Workbench provides an easy to use interface for performing the many tasks involved when working with databases. It integrates SQL development, administration, database design, creation and maintenance into one visual integrated development environment.
MySQL Workbench is similar to SQL Server’s SSMS, which is used for administering SQL Server.
An orphaned record is a record whose foreign key value references a non-existent primary key value.
Orphaned records are a concept within database relationships. If a row in a related table references a non-existent row in the primary table, it is said to be an orphaned row. This is because it has no “parent” with which its data is associated with. The terms orphaned row and orphaned record tend to be used interchangeably, even though there’s a subtle difference between a row and a record.
Referential integrity refers to the accuracy and consistency of data within a relationship.
In relationships, data is linked between two or more tables. This is achieved by having the foreign key (in the associated table) reference a primary key value (in the primary – or parent – table). Because of this, we need to ensure that data on both sides of the relationship remain intact.
So, referential integrity requires that, whenever a foreign key value is used it must reference a valid, existing primary key in the parent table.
The term data integrity refers to the accuracy and consistency of data.
When creating databases, attention needs to be given to data integrity and how to maintain it. A good database will enforce data integrity whenever possible.
For example, a user could accidentally try to enter a phone number into a date field. If the system enforces data integrity, it will prevent the user from making these mistakes.
Maintaining data integrity means making sure the data remains intact and unchanged throughout its entire life cycle. This includes the capture of the data, storage, updates, transfers, backups, etc. Every time data is processed there’s a risk that it could get corrupted (whether accidentally or maliciously).