.. ( ) , . : . , .. .
, . , . .. , - , , , .
RESTRICT () - , . , , , .
CASCADE () - , , . . , , . - .. - ( ) , . , , .
, .
SET NULL ( NULL) - , null-. . -, null-. -, . , , .
SET DEFAULT ( ) - , , . , null-. . -, , . " " , ( null-!). , . , , . null-. -, , . , , .
|
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- . .
, .
, - " ", " ".
, :
. 4
. : "", "" .. . .
:
. 5
-- , () (). -- , , .
-- , () (). . ( "") , ( "") - . . 4.
-- , , . -- , . -- .
25.
- , . SQL - ,
SUM
AVG-
MIN-
MAX-
COUNT-
, , SELECT
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SELECT AVG()
FROM []
SELECT Count(*)
FROM []
26-29
, . , . , , , . .
SELECT SQL. , .. , , - .
SELECT
( SELECT FROM ):
SELECT *
FROM P;
, ( WHERE ):
SELECT *
FROM P
WHERE P.PNUM > 2;
( 1 - ):
SELECT P.PNUM, P.PNAME, PD.DNUM, PD.VOLUME FROM P, PD WHERE P.PNUM = PD.PNUM;
