2.1.18. Queries and Joins | Lightenna

2.1.18. Queries and Joins

Relational database allows inter-related data
SQL select FROM gives Cartesian product
WHERE clause defines join condition

SELECT proj.pnum, mgr.ssn
FROM project AS proj, employee AS mgr
WHERE proj.mgrssn = mgr.ssn;

Alternatively, explicitly define join (note type)

SELECT project.pnum, employee.ssn
FROM project INNER JOIN employee
ON project.mgrssn = employee.ssn;

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