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SQL ??

SQL ??

SQL?Structured Query Language????????????????????????????????????????RDBMS??SQL ?????????????????????????????????????????????1986??ANSI????1988??ISO???????

SQL ???

SQL ???????????

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SQL ???????

??SQL?ANSI???????????SQL???????????????????????ANSI??????????SELECT?UPDATE?DELETE?INSERT?WHERE????????????????????????????????

?????? SQL

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SQL ??

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SQL ??

SQL??????????????????Websites?????????

SELECT * FROM Websites;

?? SQL ??

• SELECT????????????
• UPDATE????????????
• DELETE????????????
• INSERT INTO?????????????
• CREATE DATABASE?????????
• CREATE TABLE???????
• ALTER TABLE????????
• DROP TABLE??????
• CREATE INDEX???????
• DROP INDEX???????

SQL SELECT ??

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SELECT column_name, column_name
FROM table_name

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SELECT name, country
FROM Websites;

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SELECT *
FROM Websites;

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SQL WHERE ??

WHERE???????????????????CN?????????

SELECT * FROM Websites WHERE country='CN';

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• ?? (=)
• ?? (>)
• ?? (<)
• ?? (LIKE)
• ?? (BETWEEN)
• ???GROUP BY?
• ???ORDER BY?

SQL ORDER BY

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SELECT column_name, column_name
FROM table_name
ORDER BY column_name, column_name

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SELECT id, name, url
FROM Websites
ORDER BY alexa;

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SELECT id, name, url
FROM Websites
ORDER BY alexa DESC;

SQL INSERT INTO

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INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);

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INSERT INTO Websites (name, url, alexa, country)
VALUES ('??', 'https://www.baidu.com/', '4', 'CN');

SQL UPDATE

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UPDATE table_name
SET column1 = value1,
    column2 = value2,
    ...
WHERE condition;

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UPDATE Websites
SET alexa = '5000', country = 'USA'
WHERE name = '????';

SQL DELETE

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DELETE FROM table_name
WHERE condition;

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DELETE FROM Websites
WHERE name = 'Facebook' AND country = 'USA';

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SQL ???????????????????????????????????????????????SQL??????????WHERE?ORDER BY?GROUP BY?????????????????