기본 SQL문 - FROM

FROM from_specification

from_specification:
table_spec [ {, table_spec | outerjoin_table_spec}...]

table_spec:
single_table_spec [ correlation ] [ WITH(lock_hint [ {, lock_hint }_ ] ) ]
( single _table_spec [ {, single_table_spec}...] )
CLASS table_name [ correlation ]
subquery correlation
TABLE (expression) correlation

outerjoin_table_spec:
{ LEFT | RIGHT } [OUTER] JOIN table_spec ON search_condition

single_table_spec:
[ ONLY ] table_name
ALL table_name [ ( EXCEPT table_spec) ]

correlation:
[ AS ] identifier

lock_hint:
READ UNCOMMITTED

FROM (subquery) [ AS ] derived_table_name [( column_name [ {, column_name }_ ] )]

SELECT SUM(n) FROM (SELECT gold FROM participant WHERE nation_code='KOR'
UNION ALL SELECT silver FROM participant WHERE nation_code='JPN') AS t(n);
=== <Result of SELECT Command in Line 2> ===
 sum(n)
=======
   82
1 rows selected.

SELECT nation_code, host_year, gold
FROM participant p
WHERE gold > ( SELECT AVG(s)
   FROM ( SELECT silver + bronze
   FROM participant
   WHERE nation_code = p.nation_code
   AND silver > 0
   AND bronze > 0
) AS t(s));
=== <Result of SELECT Command in Line 1> ===
   nation_code   host_year   gold
====================================
   'JPN'   2004   16
   'CHN'   2004   32
   'DEN'   1996   4
   'ESP'   1992   13
4 rows selected.