SQL 表名周围的引号究竟有什么作用？
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What exactly do quotation marks around the table name do?
提问by George Mauer
I thought that the quotation mark (") was simply a type of grouping marker but I'm debugging some NHibernate code and notice that while
我认为引号 (") 只是一种分组标记，但我正在调试一些 NHibernate 代码并注意到
SELECT * FROM site WHERE site_id = 3;
Works fine
工作正常
SELECT * FROM "site" WHERE site_id = 3;
fails with a table or view does not exist error.
因表或视图不存在错误而失败。
What gives?
是什么赋予了？
回答by Justin Cave
Putting double-quotes around an identifier in Oracle causes Oracle to treat the identifier as case sensitive rather than using the default of case-insensitivity. If you create a table (or a column) with double-quotes around the name, you must always refer to the identifier with double quotes and by correctly specifying the case (with the exception of all upper case identifiers, where double-quotes are meaningless).
在 Oracle 中将标识符放在双引号周围会导致 Oracle 将标识符视为区分大小写，而不是使用不区分大小写的默认值。如果您创建的表（或列）在名称周围加上双引号，则必须始终使用双引号引用标识符并正确指定大小写（所有大写标识符除外，其中双引号没有意义） ）。
Under the covers, Oracle is always doing case-sensitive identifier matching. But it always casts identifiers that are not double-quoted to upper case before doing the matching. If you put double-quotes around an identifier, Oracle skips the casting to upper case.
在幕后，Oracle 总是进行区分大小写的标识符匹配。但它总是在进行匹配之前将没有双引号的标识符转换为大写。如果在标识符周围加上双引号，Oracle 将跳过转换为大写。
So if you do something like
所以如果你做类似的事情
CREATE TABLE my_table(
col1 number,
col2 number
)
you can
你可以
SELECT * FROM my_table
SELECT * FROM MY_TABLE
SELECT * FROM My_Table
SELECT * FROM "MY_TABLE"
but something like
但像
SELECT * FROM "my_table"
will fail.
将失败。
On the other hand, if you do something like
另一方面，如果你做类似的事情
CREATE TABLE "my_other_table"(
col1 number,
col2 number
)
you cannot do
你不能做
SELECT * FROM my_other_table
SELECT * FROM MY_OTHER_TABLE
SELECT * FROM My_Other_Table
SELECT * FROM "MY_OTHER_TABLE"
but this
但是这个
SELECT * FROM "my_other_table"
will work
将工作
回答by Erich Kitzmueller
It should be added that identifiers in quotation marks may contain special characters, e.g. "a-b c.d" is a valid identifier.
需要补充的是，引号中的标识符可以包含特殊字符，例如“ab cd”是有效标识符。
