Structured Query Language (SQL)

Structured Query Language (SQL)

1. "SELECT" and "WHERE" Clauses

   • I think the project would be a good fit for an EPQ as it would be a large project and I could do a lot of evaluation on aspects such as performance on different computers and alternate solutions with different advantages and disadvantages.
     • These tables are made up of rows (records) and columns (attributes). Each piece of data representing a values for a specific record for a specific attribute is called a field.
   • Each "entity" in a database is known as a record and has multiple fields which hold data about the record.
     • Records in one table are able to refer to records in another table using "foreign keys" that represent the primary keys of records in that table that the record is related to.
     • Records are distinguished from one another by each having a unique primary key which will be contained in the first column of the table for the records.
       • Sometimes, giving each record a unique primary key in a database is not possible or easy. In this case, multiple keys can be combined to create a composite key that acts as the primary key.
   • Databases with only one table are known as flat-file databases. These are very inefficient.
     • The process of converting from a flat-file database to a relational database is known as "normalisation".
   • Databases with multiple tables with links between them are known as relational databases.

2. Syntax

   • The syntax of SQL is is very logical and close to English, making it intuitive to understand.
     • SQL commands can be broken up into clauses/statements and predicates and expressions.
       • For example, in the command "SELECT * FROM People WHERE Name = ‘John’", both "SELECT * FROM People" and "WHERE Name='John'" are clauses/statements, "Name='John'" is a predicate and "'John'" is an expression.