SQL
SQL
SQL . SQL, , .
, . !
1. SQL?
SQL Structured Query Language . , .
SQL , , . , , . , , .
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() , . , .
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. , . .
4. ?
() , , . SQL.
MySQL. PostgreSQL, Oracle DB, SQL Server SQLite.
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, . . , .
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.
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, . .
: INTEGER, TEXT, DATE, REAL.
8. ?
(primary key) , .
: (NULL), .
, customers customer_id.
(foreign key) , . , orders. . customer_id.
9. ALTER UPDATE?
ALTER . .
UPDATE . .
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(query) SQL , ., .
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(subquery) , .
SELECT, INSERT, UPDATE DELETE.
, .
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(constraints) , , . , .
, , .
:
PRIMARY KEY: . UNIQUE: . NOT NULL: . DEFAULT: , , .
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(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. ?
, .
, , .
