SQL
Advanced Practice: Subqueries, CTEs and Window Functions
Twelve harder exercises - correlated subqueries, recursive CTEs, ranking, running totals and top N per group - with solutions and the reasoning behind...
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SQL
Realistic Scenarios: Analysis and Optimisation
Six end to end problems of the kind real work produces - a sales report, a retention table, a data quality audit, a duplicate cleanup and two optimisa...
DBMS
Data, Information and Databases
Data is raw recorded fact, information is data placed in context, and a database is an organised, shared, self describing collection of related data...
DBMS
What a DBMS Is and Why It Exists
A DBMS is the software layer between users and stored data. It exists to give many users controlled, concurrent, recoverable and consistent access to...
DBMS
File System versus DBMS
The file based approach fails on redundancy, inconsistency, isolation, atomicity, concurrency, security and integrity. Each failure maps to one specif...
DBMS
Advantages and Limitations of a DBMS
A DBMS buys controlled redundancy, enforced integrity, sharing, security, recovery and independence. It charges for them in cost, complexity, hardware...
DBMS
Database Users and the Role of the DBA
A database system serves naive users, application programmers, sophisticated users and specialised users, and is run by a database administrator whose...
DBMS
Three Level Architecture and Data Abstraction
The ANSI-SPARC architecture separates a database into external, conceptual and internal levels. That separation is what makes data abstraction and dat...
DBMS
Logical and Physical Data Independence
Data independence is the ability to change a schema at one level without changing the level above. Physical independence is easy to achieve; logical i...
DBMS
Schema, Instance and Metadata
A schema is the design of a database and rarely changes. An instance is the data in it at one moment and changes constantly. Metadata is the stored de...
DBMS
Database Applications and the Database System Environment
Where databases are actually used, and what sits inside a running database system: the DBMS software, the stored database, the catalog, the applicatio...
DBMS
One Tier, Two Tier and Three Tier Architecture
Tier architecture describes how many machines or layers a database request passes through. One tier is local, two tier puts the application on the cli...