:
. (. ),
- NOT NULL - ( NULL)
- UNIQUE - PRIMARY KEY - .
- REFERNECES <__> [<_>] - , _ .
:
DROP TABLE <_>
:
| ALTER TABLE <_> ADD (<_> <_> [NOT NULL] [UNIQUE | PRIMARY KEY] [REFERENCES <__> [<_>]] ,...) | |
| ALTER TABLE <_> DROP (<_>,...) | |
| ALTER TABLE <_> MODIFY (<_> <_> [NOT NULL] [UNIQUE | PRIMARY KEY] [REFERENCES <__> <_>]] ,...) |
10) SQL .
INSERT SQL, , . values select.
, .
:
INSERT INTO <_> [ (<_>,<_>,...) ] VALUES (<>,<>,..). , CREATE TABLE, :
INSERT INTO publishers VALUES (16,"Microsoft Press","http://www.microsoft.com");:
INSERT INTO publishers (publisher,pub_id) VALUES ("Super Computer Publishing",17);
, :
INSERT INTO < > ([< >,... ]) VALUES (<>,...), :
set identity_insert
INSERT INTO < > VALUES (<>,...)select:
INSERT INTO < > SELECT < >,... FROM < >, . , insert, , null, .
|
|
|
11) SQL .
:
UPDATE <_> SET <_>=<>,... [WHERE <>]WHERE , UPDATE , . , UPDATE . :
UPDATE publishers SET url="http://www.superpub.com" WHERE pub_id=17;. :
- : >, <, >=, <=, =, <>,!=. SQL , ("<" , ">" ) ("<" ">" ).
- NULL: IS NULL, IS NOT NULL
- : BETWEEN NOT BETWEEN.
- : IN NOT IN
- : LIKE NOT LIKE
- AND, OR, NOT .
, SELECT. :
UPDATE publishers SET url="url not defined" WHERE url IS NULL;publishers url "url not defined".
DELETE FROM <_> [ WHERE <> ]
, . WHERE , . :
DELETE FROM publishers WHERE publisher = "Super Computer Publishing";Super Computer Publishing.
12) SQL .
.
SQL SELECT. "" ( ), (join) . SQL, SELECT :
SELECT [ALL | DISTINCT] <_> FROM <_>,... [ WHERE <> ] [ GROUP BY <_>,... ] [ HAVING <> ] [ORDER BY <_> [ASC | DESC],... ]SELECT (, GROUP BY ORDER BY), .
SELECT . , , publications, , , .
SELECT. <_> , . , * (), . .
|
|
|
:
SELECT author FROM authors;authors:
SELECT * FROM authors;, , , , WHERE. , , 1996 :
SELECT title FROM titles WHERE yearpub > 1996;SQL "" (UNION) , SELECT. , .: -, publications. publishers wwwsites. , , :
SELECT publisher,url FROM publishers UNION SELECT site,url FROM wwwsites;13) . . ANY, ALL, EXISTS.
SQL-
SQL (SQL-). COUNT(*) , :
COUNT
- ,
SUM
- ,
AVG
- ,
MAX
- ,
MIN
- .
