Relational database: selected writings
Relational database: selected writings
The relational model for database management: version 2
The relational model for database management: version 2
ACM SIGMOD Record
Database processing (5th ed.): fundamentals, design, and implementation
Database processing (5th ed.): fundamentals, design, and implementation
Learning SQL with a computerized tutor
SIGCSE '98 Proceedings of the twenty-ninth SIGCSE technical symposium on Computer science education
Human factors comparison of a procedural and a nonprocedural query language
ACM Transactions on Database Systems (TODS)
Online assessment of SQL query formulation skills
ACE '03 Proceedings of the fifth Australasian conference on Computing education - Volume 20
Fundamentals of Database Systems, Fourth Edition
Fundamentals of Database Systems, Fourth Edition
Learning from database performance benchmarks
Journal of Computing Sciences in Colleges
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Once students have mastered basic database querying with SQL, the next step for the instructor is to present operators that can extract complex information from multiple tables. The relational database left-outer-join (LOJ) expression (T1▹T2) is used to merge two tables, say T1 and T2, using any given condition. Unlike regular database joins, when records from the first table (T1) fail to match records in the second table (T2) the LOJ operator retains each of those T1 tuples and adds an appropriate number of "null" values to compensate for the missing contribution of T2 records. In spite of its relatively simple definition and frequency in everyday common problems, we have observed that novice database students oftentimes have difficulties in understanding and properly using this technique. In this paper, we discuss three functionally equivalent versions of the left-outer-join operator to allow multiple ways of presenting the material and to show students a single data extraction problem from three viewpoints. We have developed an empirical evaluation of perceived difficulty and manageability of those versions. A simple performance analysis is conducted to determine the relative merits of each alternative.