oracle quotes escape

Oracle is currently one of the most popular enterprise-level database management systems and is widely used in various enterprise-level application platforms. In Oracle, quotation mark escaping is a common problem because quotation marks are the marking symbols that represent string values ​​in SQL statements. If the string value itself contains quotes, they need to be escaped to avoid syntax errors. This article will introduce in detail the quotation mark escaping problem in Oracle.

1. Single quote escape

In Oracle, two types of quotes are used to represent string values: single quotes and double quotes. Among them, single quotes are usually used to represent text strings, for example:

SELECT *
FROM Employees
WHERE FirstName = 'John';

In the above code, 'John' represents a text string used to match rows with the value John in the FirstName column.

However, if the text string itself contains single quotes, a syntax error will occur, for example:

SELECT *
FROM Employees
WHERE FirstName = 'John's';

In this case, the quotes are not recognized, causing a syntax error. In order to solve this problem, you can use single quotes to escape, for example:

SELECT *
FROM Employees
WHERE FirstName = 'John''s';

In the above code, two single quotes appear continuously, indicating a single quote character.

2. Double quote escape

In addition to single quotes, Oracle also supports the use of double quotes to represent identifiers (such as table names, column names, etc.). In some cases, especially when identifiers contain unusual characters, double quote escaping is useful. For example:

SELECT "First Name", "Last Name"
FROM Employees;

In the above code, "First Name" and "Last Name" are identifiers enclosed in double quotes. In this case, double quotes preserve spaces and other special characters in the identifier.

However, it is important to note that using double quotes will cause Oracle case sensitivity, because Oracle converts identifiers to uppercase characters by default. Therefore, if an identifier enclosed in double quotes contains lowercase characters, they need to be escaped using double quotes. For example:

SELECT "First Name", "Last Name"
FROM Employees;

In the above code, "first Name" and "last Name" are identifiers enclosed in double quotes, so Oracle considers them to be different from the normal case and does not convert them are uppercase characters.

3. ANSI_QUOTES mode

Sometimes, you need to use both single quotes and double quotes in Oracle, for example:

SELECT *
FROM Employees
WHERE "First Name" = 'John';

In the above code," First Name" is an identifier enclosed in double quotes, while 'John' is a text string enclosed in single quotes.

However, Oracle does not support mixing single and double quotes by default. If you want to use ANSI_QUOTES mode in Oracle to support this situation, you need to use the following command:

SET SQL92_RESERVED_WORDS = 'NONE';

After using the above command, Oracle can support the mixed use of single quotes and double quotes.

4. Summary

In Oracle, quotation mark escaping is a very common problem. If you want to use single quotes to represent a text string, you need to note that the text string may contain single quotes, and you can use two consecutive single quotes to escape. If you want to use double quotes to represent identifiers, you need to note that Oracle converts identifiers to uppercase characters by default and can be escaped using double quotes. If you need to use both single and double quotes, you can use ANSI_QUOTES mode. The above are the basic knowledge points about quotation mark escaping in Oracle. I hope it will be helpful to readers.

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