How Do Quotation Marks Affect Case Sensitivity and Access to Oracle Table Names?

The role of quotation marks in table names in Oracle database

In Oracle Database, quotes play an important role in table naming conventions and case sensitivity. Unlike their primary function as grouping markers, quotes around table names have specific meaning for table access and data manipulation.

Case sensitivity and quotation marks

By default, Oracle treats identifiers (including table names) as case-insensitive. However, enclosing an identifier in double quotes makes it case-sensitive. For example, if you create a table named "SITE" (with double quotes), you must always refer to it using double quotes and the exact case specified.

For example, the following query will return the expected results:

<code class="language-sql">SELECT * FROM "SITE" WHERE SITE_ID = 3;</code>

However, queries without quotes or incorrect capitalization will fail:

<code class="language-sql">SELECT * FROM SITE WHERE SITE_ID = 3; -- 失败
SELECT * FROM "site" WHERE SITE_ID = 3; -- 失败</code>

The mechanism behind the scenes

Internally, Oracle applies case-insensitive conversion (conversion to uppercase) to unquoted identifiers. For quoted identifiers, this conversion is skipped, ensuring case-sensitive matching.

Practical Application

Using quotes for table names may be beneficial in the following situations:

• Keep keywords as identifiers when table names may conflict with SQL keywords.
• Enhance clarity and consistency when case-sensitive database objects need to be distinguished.

Example

Consider two tables: SITE and site. Without quotes, both tables will be interpreted as the same table "SITE". However, use quotes:

<code class="language-sql">CREATE TABLE "SITE"(ID INT, NAME VARCHAR2(100));
CREATE TABLE "site"(ID INT, ACTIVE BOOLEAN);</code>

These tables can be uniquely identified and accessed:

<code class="language-sql">SELECT * FROM "SITE";
SELECT * FROM "site";</code>

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