SQL语法祥解.docx

1、SQL语法祥解SQL语法详解 例： “Persons” 表中的数据有LastName FirstName Address CityHansen Ola Timoteivn 10 SandnesSvendson Tove Borgvn 23 SandnesPettersen Kari Storgt 20 StavangeSelect用途：从指定表中取出指定的列的数据语法：SELECT column_name(s) FROM table_name解释：从数据库中选取资料列，并允许从一或多个资料表中，选取一或多个资料列或资料行。SELECT 陈述式的完整语法相当复杂，但主要子句可摘要为：SELECT

2、 select_list INTO new_table FROM table_source WHERE search_condition GROUP BY group_by_expression HAVING search_condition ORDER BY order_expression ASC | DESC 选出字段名” LastName”、” FirstName” 的数据SELECT LastName,FirstName FROM Persons 返回结果:LastNameFirstNameHansenOlaSvendsonTovePettersenKa选出所有字段的数据SELECT

3、 * FROM Persons返回结果:LastNameFirstNameAddressCityHansenOlaTimoteivn 10SandnesSvendsonToveBorgvn 23SandnesPettersenKariStorgt 20StavangWhere用途：被用来规定一种选择查询的标准语法：SELECT column FROM table WHERE column condition &118;alue下面的操作符能被使用在WHERE中：=,=,=,BETWEEN,LIKE注意： 在某些SQL的版本中不等号能被写作为!=解释：SELECT语句返回WHERE子句中条件为t

4、rue的数据例：从” Persons”表中选出生活在” Sandnes” 的人SELECT * FROM Persons WHERE City=Sandnes返回结果:LastName FirstName Address City YearHansen Ola Timoteivn 10 Sandnes 1951Svendson Tove Borgvn 23 Sandnes 1978Svendson Stale Kaivn 18 Sandnes 1980And & Or用途：在WHERE子句中AND和OR被用来连接两个或者更多的条件解释：AND在结合两个布尔表达式时，只有在两个表达式都为 TRU

5、E 时才传回 TRUEOR在结合两个布尔表达式时，只要其中一个条件为 TRUE 时，OR便传回 TRUE例：Persons 表中的原始数据:LastName FirstName Address CityHansen Ola Timoteivn 10 SandnesSvendson Tove Borgvn 23 SandnesSvendson Stephen Kaivn 18 Sandnes用AND运算子来查找Persons 表中FirstName为”Tove”而且LastName为” Svendson”的数据SELECT * FROM PersonsWHERE FirstName=ToveAN

6、D LastName=Svendson返回结果:LastName FirstName Address CitySvendson Tove Borgvn 23 Sandnes用OR运算子来查找Persons 表中FirstName为”Tove”或者LastName为” Svendson”的数据SELECT * FROM PersonsWHERE firstname=ToveOR lastname=Svendson返回结果:LastName FirstName Address CitySvendson Tove Borgvn 23 SandnesSvendson Stephen Kaivn 18

7、Sandnes你也能结合AND和OR (使用括号形成复杂的表达式),如:SELECT * FROM Persons WHERE(FirstName=Tove OR FirstName=Stephen)AND LastName=Svendson返回结果:LastName FirstName Address CitySvendson Tove Borgvn 23 SandnesSvendson Stephen Kaivn 18 SandnesBetweenAnd用途：指定需返回数据的范围语法：SELECT column_name FROM table_nameWHERE column_nameBE

8、TWEEN &118;alue1 AND &118;alue2例：“Persons”表中的原始数据LastNameFirstNameAddressCityHansenOlaTimoteivn 10SandnesNordmannAnnaNeset 18SandnesPettersenKariStorgt 20StavangerSvendsonToveBorgvn 23Sandnes用BETWEENAND返回LastName为从”Hansen”到”Pettersen”的数据：SELECT * FROM Persons WHERE LastName BETWEEN Hansen AND Petter

9、sen返回结果:LastNameFirstNameAddressCityHansenOlaTimoteivn 10SandnesNordmannAnnaNeset 18SandnesPettersenKariStorgt 20Stavanger为了显示指定范围之外的数据，也可以用NOT操作符：SELECT * FROM Persons WHERE LastName NOT BETWEEN Hansen AND Pettersen返回结果:LastName FirstName Address CitySvendson Tove Borgvn 23 SandnesDistinct用途：DISTIN

10、CT关键字被用作返回唯一的值语法：SELECT DISTINCT column-name(s) FROM table-name解释：当column-name(s)中存在重复的值时，返回结果仅留下一个例：“Orders”表中的原始数据CompanyOrderNumberSega3412W3Schools2312Trio4678W3Schools679用DISTINCT关键字返回Company字段中唯一的值：SELECT DISTINCT Company FROM Orders返回结果:Company SegaW3Schools TrioOrder by用途：指定结果集的排序语法：SELECT c

11、olumn-name(s) FROM table-name ORDER BY order_by_expression ASC | DESC 解释：指定结果集的排序，可以按照ASC(递增方式排序，从最低值到最高值)或者DESC(递减方式排序，从最高值到最低值)的方式进行排序，默认的方式是ASC例：“Orders”表中的原始数据:CompanyOrderNumberSega3412ABC Shop5678W3Schools2312W3Schools6798按照Company字段的升序方式返回结果集：SELECT Company, OrderNumber FROM OrdersORDER BY Co

12、mpany返回结果:CompanyOrderNumberABC Shop5678Sega3412W3Schools6798W3Schools2312按照Company字段的降序方式返回结果集：SELECT Company, OrderNumber FROM OrdersORDER BY Company DESC返回结果:CompanyOrderNumberW3Schools6798W3Schools2312Sega3412ABC Shop5678Group by用途：对结果集进行分组，常与汇总函数一起使用。语法：SELECT column,SUM(column) FROM table GROU

13、P BY column例：“Sales”表中的原始数据:CompanyAmountW3Schools5500IBM4500W3Schools7100按照Company字段进行分组，求出每个Company的Amout的合计：SELECT Company,SUM(Amount) FROM SalesGROUP BY Company返回结果：CompanySUM(Amount)W3Schools12600IBM4500Having用途：指定群组或汇总的搜寻条件。语法：SELECT column,SUM(column) FROM tableGROUP BY columnHAVING SUM(colum

14、n) condition &118;alue解释：HAVING 通常与 GROUP BY 子句同时使用。不使用 GROUP BY 时，HAVING 则与 WHERE 子句功能相似。例：“Sales”表中的原始数据:CompanyAmountW3Schools5500IBM4500W3Schools7100按照Company字段进行分组，求出每个Company的Amout的合计在10000以上的数据：SELECT Company,SUM(Amount) FROM SalesGROUP BY Company HAVING SUM(Amount)10000返回结果：Company SUM(Amoun

15、t)W3Schools 12600Join用途：当你要从两个或者以上的表中选取结果集时，你就会用到JOIN。例：“Employees”表中的数据如下，（其中ID为主键）:IDName01Hansen, Ola02Svendson, Tove03Svendson, Stephen04Pettersen, Kar“Orders”表中的数据如下：IDProduct01Printer03Table03Chai用Employees的ID和Orders的ID相关联选取数据：SELECT Employees.Name, Orders.ProductFROM Employees, OrdersWHERE Em

16、ployees.ID = Orders.ID返回结果：NameProductHansen, OlaPrinterSvendson, StephenTableSvendson, StephenChair或者你也可以用JOIN关键字来完成上面的操作：SELECT Employees.Name, Orders.ProductFROM EmployeesINNER JOIN OrdersON Employees.ID = Orders.IDINNER JOIN的语法：SELECT field1, field2, field3FROM first_tableINNER JOIN second_table

17、ON first_table.keyfield = second_table.foreign_keyfield解释：INNER JOIN返回的结果集是两个表中所有相匹配的数据。LEFT JOIN的语法：SELECT field1, field2, field3FROM first_tableLEFT JOIN second_tableON first_table.keyfield = second_table.foreign_keyfield用”Employees”表去左外联结”Orders”表去找出相关数据：SELECT Employees.Name, Orders.ProductFROM

18、EmployeesLEFT JOIN OrdersON Employees.ID = Orders.ID返回结果：NameProductHansen, OlaPrinterSvendson, ToveSvendson, StephenTableSvendson, StephenChairPettersen, Kari解释：LEFT JOIN返回”first_table”中所有的行,尽管在” second_table”中没有相匹配的数据。RIGHT JOIN的语法：SELECT field1, field2, field3FROM first_tableRIGHT JOIN second_tab

19、leON first_table.keyfield = second_table.foreign_keyfield用”Employees”表去右外联结”Orders”表去找出相关数据：SELECT Employees.Name, Orders.ProductFROM EmployeesRIGHT JOIN OrdersON Employees.ID = Orders.ID返回结果：NameProductHansen, OlaPrinterSvendson, StephenTableSvendson, StephenChai解释：RIGHT JOIN返回” second_table”中所有的行尽

20、管在”first_table”中没有相匹配的数据。Alias用途： 可用在表、结果集或者列上，为它们取一个逻辑名称语法：给列取别名：SELECT column AS column_alias FROM table给表取别名：SELECT column FROM table AS table_alias例：“Persons”表中的原始数据:LastName FirstName Address CityHansen Ola Timoteivn 10 SandnesSvendson Tove Borgvn 23 SandnesPettersen Kari Storgt 20 Stavanger运行下

21、面的SQL：SELECT LastName AS Family, FirstName AS NameFROM Persons返回结果：FamilyNameHansenOlaSvendsonTovePettersenKar运行下面的SQL：SELECT LastName, FirstNameFROM Persons AS Employees返回结果：Employees中的数据有：LastNameFirstNameHansenOlaSvendsonTovePettersenKariInsert Into用途： 在表中插入新行语法：插入一行数据INSERT INTO table_namevalues

22、 (&118;alue1, &118;alue2,.)插入一行数据在指定的字段上INSERT INTO table_name (column1, column2,.)values (&118;alue1, &118;alue2,.)例：“Persons”表中的原始数据:LastName FirstName Address CityPettersen Kari Storgt 20 Stavanger运行下面的SQL插入一行数据：INSERT INTO Personsvalues (Hetland, Camilla, Hagabakka 24, Sandnes)插入后”Persons”表中的数据为

23、：LastName FirstName Address CityPettersen Kari Storgt 20 StavangerHetland Camilla Hagabakka 24 Sandnes运行下面的SQL插入一行数据在指定的字段上：INSERT INTO Persons (LastName, Address)values (Rasmussen, Storgt 67)插入后”Persons”表中的数据为：LastName FirstName Address CityPettersen Kari Storgt 20 StavangerHetland Camilla Hagabakk

24、a 24 SandnesRasmussen Storgt 67Update用途：更新表中原有数据语法：UPDATE table_name SET column_name = new_&118;alueWHERE column_name = some_&118;alue例：“Person”表中的原始数据:LastName FirstName Address CityNilsen Fred Kirkegt 56 StavangerRasmussen Storgt 67运行下面的SQL将Person表中LastName字段为”Rasmussen”的FirstName更新为”Nina”：UPDATE

25、Person SET FirstName = NinaWHERE LastName = Rasmussen更新后”Person”表中的数据为：LastName FirstName Address CityNilsen Fred Kirkegt 56 StavangerRasmussen Nina Storgt 67同样的，用UPDATE语句也可以同时更新多个字段：UPDATE PersonSET Address = Stien 12, City = StavangerWHERE LastName = Rasmussen更新后”Person”表中的数据为：LastName FirstName A

26、ddress CityNilsen Fred Kirkegt 5 StavangerRasmussen Nina Stien 12 StavangerDelete用途：删除表中的数据语法：DELETE FROM table_name WHERE column_name = some_&118;alue例：“Person”表中的原始数据:LastName FirstName Address CityNilsen Fred Kirkegt 56 StavangerRasmussen Nina Stien 12 Stavanger删除Person表中LastName为”Rasmussen”的数据：D

27、ELETE FROM Person WHERE LastName = Rasmussen执行删除语句后”Person”表中的数据为：LastName FirstName Address CityNilsen Fred Kirkegt 56 StavangerCreate Table用途：建立新的资料表。语法：CREATE TABLE table_name(column_name1 data_type,column_name2 data_type,.)例：创建一张叫“Person”的表，该表有4个字段LastName, FirstName, Address, Age：CREATE TABLE P

28、erson(LastName varchar,FirstName varchar,Address varchar,Age int)如果想指定字段的最大存储长度，你可以这样：CREATE TABLE Person(LastName varchar(30),FirstName varchar(30),Address varchar(120),Age int(3)下表中列出了在SQL的一些数据类型：Data TypeDescriptioninteger(size)int(size)smallint(size)tinyint(size)Hold integers only. The maximum number of digits are specified in parenthesis.decimal(size,d)numeric(size,d)Hold numbers with fractions. The maximum number of digits are specified in size. The maximum number of d