SQL
SQL
SQL . SQL, , .
, . !

1. SQL?
SQL Structured Query Language . , .
SQL , , . , , . , , .
2. ?
() , . , .
3. ?
. , . .
4. ?
() , , . SQL.
MySQL. PostgreSQL, Oracle DB, SQL Server SQLite.
5. ?
, . . , .
6. ?
.
.
7. ?
, . .
: INTEGER
, TEXT
, DATE
, REAL
.
8. ?
(primary key) , .
: (NULL
), .
, customers
customer_id
.
(foreign key) , . , orders
. . customer_id
.
9. ALTER UPDATE?
ALTER
. .
UPDATE
. .
10. ?
(query) SQL , ., .
11. ?
(subquery) , .
SELECT
, INSERT
, UPDATE
DELETE
.
, .
12. ?
(constraints) , , . , .
, , .
:
PRIMARY KEY
: . UNIQUE
: . NOT NULL
: . DEFAULT
: , , .
13. ?
(statement) , .
, , .
, (;
). . ( ).
14. , ?
, NULL
.
, IS NULL: WHERE [] IS NULL
.
, IS NOT NULL: WHERE [] IS NOT NULL
.
15. DISTINCT UNIQUE?
DISTINCT
, , . .
UNIQUE
, , . PRIMARY KEY
, , UNIQUE
.
16. ?
.
: COUNT()
, SUM()
, MAX()
, MIN()
, AVG()
ROUND()
.
17. (JOIN)?
JOIN
.
18. INNER JOIN LEFT JOIN?
INNER JOIN
, ON
. , ON
.
LEFT JOIN
, , ON
.
19. ?
(windows functions) , . , , .
20. ?
, .
, , .