What technique is used to retrieve data from more than one
table in a single SQL statement?
Answer Posted / mani
Both UNION or UNION ALL and JOIN can be used.
The purpose of retreiving data from more than one table in a
single statement generally happens when the ouput of the
involved tables has same table structure and in this case
either UNION (to eliminate the duplicates in the resultant
table)or UNION ALL (to retain the duplicates in the
resultant table)could be used.
If retrieval is based on seletion criterion then JOINS could
also be used but here the resultant table structure can be
different from that of the tables involved in join operation.
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