SQL ,
. SQL Structured Query Language . SQL , .
SQL , -
.
- SQL . , .. . . SQL- :
-
-
-
-- ,
-- .
SQL (), ,
. SQL
, , :
(Data Manipulation Language, DML);
(Data Definition Language, DDL);
(Data Control Language, DCL).
, .
.
(DML, ) -
:
SELECT () ;
INSERT () ;
UPDATE () ;
DELETE () .
(DDL, )
(CREATE ), (ALTER), (DROP) , , ( ), . :
CREATE INDEX ; ALTER INDEX ; DROP INDEX ; DROP TABLE ;
(DCL)
. . :
GRANT ; REVOKE .
SQL: . SQL , . SQL (, SQL Explorer).
SQL ,
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, .
, -
.
: (Restriction), (Projection), (Join), (Union), , , (Cross Join).
, . , .. , . , , .
, country:
SELECT * FROM country
-
, .. . , -.
, , vendors:
SELECT VendorName,City,Country FROM vendors
. . , , Roger:
SELECT firstName,lastName FROM employee
WHERE firstName="Roger"
R×S ( )
R S.
R 1, 2 S b1, b2. SELECT R.a1, R.a2, S.b1, S.b2 FROM R,S -
, N K , M L , N×M K+L .
(UNION) -
. , UNION SQL- . , . . :
. employee country , :
SELECT first_name,last_name,job_country FROM employee
WHERE job_country = "France"
UNION
SELECT contact_first,contact_last,country FROM customer
WHERE country = "France"
36. SQL. SELECT: , .
SELECT SQL. , . :
SELECT (*/(.1),(.2)/)- .
FROM (.1),(.2) - ().
WHERE ( () )
SELECT SQL- , .
SELECT FROM. . FROM , . , , .
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, . . (), "*". , , , : < >.< >.
