How Can I Efficiently Check for NULL and Empty Strings in PostgreSQL?

Best Practices for NULL and Empty String Checking in PostgreSQL

Check for NULL or empty value

When dealing with string values ​​in PostgreSQL, be sure to check for NULL values ​​(indicating no data at all) and empty strings (indicated by ''). A common approach is to use the coalesce function:

coalesce(stringexpression, '')=''

However, this approach can be verbose and inefficient, especially if the expression to be checked is complex.

Efficient and concise NULL and empty string checking

A more efficient and concise solution is to utilize comparison operators:

(stringexpression = '') IS NOT FALSE

This expression checks whether stringexpression is equal to the empty string or NULL. The result will be:

• True: if stringexpression is an empty string or NULL.
• Null: If stringexpression is NULL.
• False: Otherwise.

This method works particularly well for character types such as char(n), where an empty string is indistinguishable from a string consisting only of spaces.

Check for non-NULL and non-null values

To assert the opposite, just use:

stringexpression <> ''

Notes on char(n)

The char(n) data type requires special attention. By design, empty strings in char(n) are padded with spaces to reach the specified length. Therefore, the above test also works for char(n).

Demo

To illustrate these methods, consider the following table:

SELECT * FROM test_data(
    VALUES
        ('foo', 'bar', NULL, '', '   ')
);

Performing various tests produces the following results:

表达式	foo	bar	NULL
stringexpression = ''	False	False	NULL	True	True
(stringexpression = '') IS NOT FALSE	False	False	True	True	True
(stringexpression '') IS NOT TRUE	True	True	False	False	False
coalesce(stringexpression, '') = ''	False	False	True	False	True

Conclusion

The efficient and concise approach outlined above provides a powerful and reliable solution when checking for NULL or null values ​​in PostgreSQL. By using comparison operators, you can get the results you want without the overhead of using clumsy expressions.

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