Tags

links:
http://en.wikipedia.org/wiki/DUAL_table
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1562813956388
http://dba.stackexchange.com/questions/28528/why-do-i-have-to-select-from-the-dual-table

summary:
– e.g. “SELECT order_seq.nextval FROM dual ”
– SQL standard require “TABLE” (?) so need a dummy one if not exists
– originally DUAL table had 2 rows (hence dual), but subsequently became 1 row 1 column varchar2 table
– DUAL is owned by SYS
– more a stub for query that requires a table
– logical table no physical IO anymore

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