Convert Blank Strings To NULL

Normalize empty or whitespace-only text values to `NULL` with `NULLIF(TRIM(...), '')`.

Created May 10, 2026 Last updated May 10, 2026 5/5 supported engines validation-green 1 example 2 scenarios

Docker-validated Not currently validation-green

Example 1

Clean blank email values

Ada's email keeps its meaningful value but loses the surrounding spaces. Bob's empty string and Cara's spaces become NULL after trimming. Dan was already NULL, and TRIM(NULL) remains NULL.

Source table data Rows loaded before the example query runs.

Setup

CREATE TABLE contacts (id INT, name VARCHAR(50), email VARCHAR(100));

INSERT INTO
  contacts
VALUES
  (1, 'Ada', ' [email protected] '),
  (2, 'Bob', ''),
  (3, 'Cara', '   '),
  (4, 'Dan', NULL);

Validated query Shared across supported engines.

SQL

UPDATE contacts
SET
  email = NULLIF(TRIM(email), '');

SELECT
  id,
  name,
  email
FROM
  contacts
ORDER BY
  id;

Expected result Returned rows for the shared example.

id	name	email
1	Ada	[email protected]
2	Bob	NULL
3	Cara	NULL
4	Dan	NULL

Supported engines share the same `UPDATE`, `TRIM`, and `NULLIF` expression here.

Useful when

Where this command helps.

cleaning imported contact fields that contain empty strings instead of nulls
normalizing optional text columns before adding data quality checks

Explanation

What the command is doing.

Blank strings and NULL often mean the same thing to users but behave differently in SQL. A cleanup update can trim accidental spaces and convert empty results to NULL, giving downstream queries one consistent missing-value representation. The NULLIF(TRIM(col), '') expression keeps meaningful text, removes edge whitespace, and turns blank values into NULL.

Convert Blank Strings To NULL

Clean blank email values

Where this command helps.

What the command is doing.

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