PostgreSQL - Dollar-Quoted String Constants

In PostgreSQL, dollar-quoted string constants, also known as dollar-quoting, provide a way to include string literals and escape sequences in SQL scripts without the need to escape single quotes or backslashes. Dollar-quoting is particularly useful when writing functions or complex SQL statements, as it avoids common escaping issues.

Basic Syntax:

A dollar-quoted string constant is specified with $$ or between two dollar signs with an optional "tag" in between. The format is:

$tag$your string content here$tag$

Examples:

Simple dollar-quoting:

SELECT $$Hello, World!$$;

Dollar-quoting with a tag:

SELECT $example$Hello, World!$example$;

Using dollar-quoting in function creation:

Without dollar-quoting:

CREATE FUNCTION example() RETURNS text AS '
  BEGIN
    RETURN ''Hello, World!'';
  END;
' LANGUAGE plpgsql;

With dollar-quoting:

CREATE FUNCTION example() RETURNS text AS $$
  BEGIN
    RETURN 'Hello, World!';
  END;
$$ LANGUAGE plpgsql;

Using dollar-quoting makes it clearer and eliminates the need for doubling up single quotes.

Using dollar-quoting for strings with special characters:

If your string content has single quotes or backslashes, dollar-quoting simplifies things:

SELECT $$It's a "special" day.\nLet's celebrate!$$;

This returns:

It's a "special" day.\nLet's celebrate!

Benefits:

Readability: Dollar-quoting can improve the readability of SQL scripts, especially when creating or modifying stored procedures and functions.
Simplifies escaping: Eliminates the need for multiple escape sequences in long strings or when writing procedural code.
Flexibility with tags: You can use custom tags to further distinguish different sections of dollar-quoted strings, making the code clearer.

Remember that dollar-quoting is a feature specific to PostgreSQL, so it might not be available or might work differently in other database systems. When using dollar-quoting, it's important to ensure the chosen delimiter (the tag) does not appear within the string content itself to avoid unexpected issues.

Using dollar-quoted strings for escaping characters in PostgreSQL:
- Description: Utilize dollar-quoted strings to handle special characters without escaping.
- Code:
```
SELECT $$This is a dollar-quoted string with 'single quotes'$$ AS result;
```
Multiline string constants in PostgreSQL with dollar quotes:
- Description: Create multiline string constants for better readability.
- Code:
```
SELECT $$
This is a
multiline
string
$$
AS result;
```
Benefits and use cases of dollar-quoted string constants in PostgreSQL:
- Description: Dollar-quoted strings simplify the use of quotes and multiline strings, improving code readability.
- Code:
```
SELECT $$
Benefits and
use cases of
dollar-quoted strings
$$
AS result;
```
Using different delimiter symbols with dollar-quoted strings in PostgreSQL:
- Description: Choose a different delimiter for dollar-quoted strings.
- Code:
```
SELECT $custom$
Using a custom delimiter
with dollar-quoted strings
$custom$ AS result;
```
Combining dollar-quoted strings with string functions in PostgreSQL:
- Description: Use dollar-quoted strings with string functions for complex string manipulations.
- Code:
```
SELECT $$
Concatenating
strings with
dollar quotes
$$ || ' in PostgreSQL' AS result;
```
Dollar-quoted strings vs standard single-quoted strings in PostgreSQL:
- Description: Compare the use of dollar-quoted strings and standard single-quoted strings.
- Code:
```
SELECT 'Standard single-quoted string' AS standard,
       $$Dollar-quoted string$$ AS dollar_quoted;
```