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Translating SQL Queries into Relational Algebra

Query Blocks

Example

What are the names of members who received messages from Cephalophore? Order alphabetically.

Here is an implementation using a nested query (this is correct but hideous):

Query blocks are color-coded.
select name from member where member_id in ( select to_member_id from routing where from_member_id = ( select member_id from member where name = 'Cephalaphore')) order by name

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