How to Efficiently Check for Null or Empty Strings in PostgreSQL?

Optimizing Null and Empty String Checks in PostgreSQL

PostgreSQL queries often require checking for null or empty strings. While coalesce() offers a solution, it can be less elegant. This article presents a more efficient and concise method.

Best Practices: Direct String Comparison

The most effective approach uses direct string comparison: stringexpression = ''. This provides clear results:

• true: For empty strings ('') or strings containing only spaces (with char(n)).
• null: For null values.
• false: For all other strings.

Conditional Expressions

To check if a string is null or empty:

• (stringexpression = '') IS NOT FALSE
• (stringexpression <> '') IS NOT TRUE

To check if a string is neither null nor empty:

• stringexpression <> ''

char(n) Data Type Behavior

Remember that char(n) treats empty strings and space-only strings as equivalent. The above expressions work seamlessly with char(n).

Example

<code class="language-sql">SELECT 'foo'::char(5) = ''::char(5) AS eq1, ''::char(5) = '  '::char(5) AS eq2, ''::char(5) = '    '::char(5) AS eq3;</code>

Output:

<code>eq1 | eq2 | eq3
---- | ---- | ----
t   | t   | t</code>

Summary

Using stringexpression = '' provides a clean and efficient way to handle null and empty string checks in PostgreSQL, especially when considering the behavior of the char(n) data type. This simplifies your queries and improves readability.

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