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SQL??? Structured Query Language???????????????????????????????????????????????????????
?? ORACLE?DB2?Sybase?SQLServer?MySQL?MS Access????????????????????????????????????????????????????????????????????????????????????????????SQL???????
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SQL??????
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???????????????????SQL Sever?????MySQL?????????????????????????????????2????SQL??????1?????SQL Sever?????????MySQL????????????????????????????MySQL?SQL Sever??????
????????SQL?????????????????????SQL????????????????????Excel????????????????????w3school?????????????????????
SQL????
1?????MySQL???????phpstudy????????mysql??????????????
2???????phpstudy???phpstudy?????????????????????????
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3?????Navicat??
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4???Navicat???????
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5???????????????????????
6????5?????????
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7???sql?????
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8?????
??????????????????w3c?sql??????
9?????
????sql????????????????
???sql??????????sql???????????????????????????????w3c?sql????????????????????
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1?CREATE TABLE????
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2?INSERT(??)
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3?UPDATE(??)
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4?DELETE(??)
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???delete??emp??????????????????????????????emp?id??orders?????????emp???id?????orders??????
5?DISTINCT????
???????????????????????????????????????????distinct???????????????????
???distinct?????????????*?????????? ????????????SQL?????????????name????????????????????distinct????????.
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6?Select????
SELECT ??????????????????????????????????????????????90%?
SQL SELECT ??
SELECT ??? FROM ???
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SELECT * FROM ???
??????? ?LastName? ? ?FirstName? ????????? ?Persons? ??????????????? SELECT ???
SELECT LastName,FirstName FROM Persons
SELECT??????????????
SQL????
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1?AVG??
AVG ????????????NULL ?????????
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2?COUNT()
COUNT( ) ????????????????
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3?MAX()
MAX????????????NULL????????
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4?MIN()
MIN?????????????NULL????????
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5?SUM()
SUM??????????
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6?ROUND()
ROUND ???????????????????
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7?FORMAT()
FORMAT ???????????????
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SQL????
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1?LIMIT
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2?LIKE
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???????????????%??????????????????like ????????
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3?IN
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4?JOIN
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??????????????primary key?????foreign key?????????
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??????????????????????????INNER JOIN??
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- LEFT JOIN:????????????????????
- RIGHT JOIN????????????????????
- FULL JOIN:????????????????
5?ALTER
??????alter??????????????alter?????
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6?UNION
UNION ???????????? SELECT ???????
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UNION?UNION ALL??????????????ALL???????????
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??????????????????PRIMARY KEY????????????????????????
?PRIMARY KEY????????????? UNIQUE ????????????? PRIMARY KEY ???
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7?AUTO-INCREMENT(??)
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8?ORDER BY
????????????order by?SQL???order by???????????????????ASC???????????
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- ASC:????????
- DESC:????????
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??DESC????????????????????SQL????
9?GROUP BY
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10?HAVING
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11?DEFAULT
DEFAULT?????????????
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