Select..docx

Select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 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 ] ]例：?“Persons”?表中的数据有LastNameFirstNameAddressCityHansenOlaTimoteivn 10SandnesSvendsonToveBorgvn 23SandnesPettersenKariStorgt 20Stavanger选出字段名”?LastName”、”?FirstName”?的数据SELECT LastName,FirstName FROM Persons返回结果:LastNameFirstNameHansenOlaSvendsonTovePettersenKari选出所有字段的数据SELECT * FROM Persons返回结果:?LastNameFirstNameAddressCityHansenOlaTimoteivn 10SandnesSvendsonToveBorgvn 23SandnesPettersenKariStorgt 20Stavanger???Where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 value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true的数据例：从”?Persons”表中选出生活在” Sandnes”?的人SELECT * FROM Persons WHERE City=Sandnes?Persons?表中的数据有:LastNameFirstNameAddressCityYearHansenOlaTimoteivn 10Sandnes1951SvendsonToveBorgvn 23Sandnes1978SvendsonStaleKaivn 18Sandnes1980PettersenKariStorgt 20Stavanger1960返回结果:LastNameFirstNameAddressCityYearHansenOlaTimoteivn 10Sandnes1951SvendsonToveBorgvn 23Sandnes1978SvendsonStaleKaivn 18Sandnes1980???And 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?TRUE?时才传回?TRUE??OR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:LastNameFirstNameAddressCityHansenOlaTimoteivn 10SandnesSvendsonToveBorgvn 23SandnesSvendsonStephenKaivn 18Sandnes??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=ToveAND LastName=Svendson返回结果:LastNameFirstNameAddressCitySvendsonToveBorgvn 23Sandnes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:LastNameFirstNameAddressCitySvendsonToveBorgvn 23SandnesSvendsonStephenKaivn 18Sandnes??你也能结合AND和OR (使用括号形成复杂的表达式),如:SELECT *