6

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. ?

, .

, , .


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