Aliasing the Table Twice (e and m)

Concepts covered: sqlSelfJoin

The query has the same shape every time. Same table in the FROM clause twice, with two different aliases. Join condition expresses the relationship between the two roles. SELECT pulls columns from both aliases. The aliases are not decoration; they are the only way SQL knows which copy of the table you are talking about in each column reference. The query you should be able to write from memory Read this query out loud while you type it. The FROM clause lists employees twice. Alias e is the employee row. Alias m is the manager row. The join condition says 'pair each employee with the row whose employee_id equals this employee's manager_id.' The WHERE filters down to pairs where the employee's salary exceeds the manager's. Without the aliases, SQL cannot tell which copy of the table you mean

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