How Do Quotation Marks Affect Table Names in Oracle?

Oracle Table Names: The Significance of Quotation Marks

A frequent question in Oracle database management involves the use of double quotes around table names. While seemingly simple, understanding their function is crucial for avoiding common errors.

Oracle's default behavior is case-insensitive identifier handling. This means MyTable, mytable, and MYTABLE are all treated as the same table. However, enclosing a table name in double quotes changes this.

Double quotes enforce case-sensitivity. "MyTable" is distinct from "mytable" or "MYTABLE". If created with quotes, the table must be referenced with the exact same casing and quotes.

Consider these examples:

<code class="language-sql">SELECT * FROM mytable WHERE id = 1; -- Works (case-insensitive)</code>

This query succeeds due to Oracle's default case-insensitive matching. But this fails:

<code class="language-sql">SELECT * FROM "mytable" WHERE id = 1; -- Fails (case-sensitive)</code>

This error arises because "mytable" was defined as case-sensitive. The query needs the exact capitalization and quotes.

Oracle internally uses case-sensitive comparisons, but it uppercases unquoted identifiers before comparison. Quoting bypasses this.

Creating a table with quotes:

<code class="language-sql">CREATE TABLE "my_data"(col1 NUMBER, col2 VARCHAR2(255));</code>

These queries are valid:

<code class="language-sql">SELECT * FROM "my_data";
SELECT * FROM "MY_DATA";
SELECT * FROM "My_Data";</code>

This, however, will fail:

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

Conversely, creating a table without quotes:

<code class="language-sql">CREATE TABLE my_other_data(col1 NUMBER, col2 VARCHAR2(255));</code>

These queries are all incorrect:

<code class="language-sql">SELECT * FROM My_Other_Data;
SELECT * FROM "my_other_data";
SELECT * FROM "MY_OTHER_DATA";</code>

Only this works:

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

Mastering the difference between case-sensitive (quoted) and case-insensitive (unquoted) identifiers and the role of double quotes is essential for effective Oracle database management and query writing.

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