Clarify self-join query execution order in lesson 14#27
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harjeet2020 wants to merge 1 commit intobtholt:mainfrom
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Clarify self-join query execution order in lesson 14#27harjeet2020 wants to merge 1 commit intobtholt:mainfrom
harjeet2020 wants to merge 1 commit intobtholt:mainfrom
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Explain why AND c2.language = 'en' join condition is necessary
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The query in lesson 14 (self-join) is somewhat confusing;
ON ... AND c2.language = 'en'andWHERE ... c2.language IS NULLseem like contradictory checks at first glance. I added a blockquote with an explanation that the join condition happens first, and that it is crucial for the query - otherwise each row would just match to itself, and final query would always return 0 rows.