How can SQLite require a value while still allowing an empty string?

If an empty string is valid, declare the column NOT NULL and don’t add a check that rejects zero-length text. NOT NULL rejects SQL NULL, but by itself it does not reject an empty string. [S1]

For example:

CREATE TABLE notes (
  label TEXT NOT NULL
);

With this table definition, NULL is rejected, while '' and 'draft' are allowed. The important distinction is that NULL is a missing SQL value, whereas '' is a text value with no characters. Choose the rule based on what your application means by “required.”

Add a length check alongside NOT NULL:

CREATE TABLE notes (
  label TEXT NOT NULL CHECK (length(label) > 0)
);

NOT NULL rejects a missing SQL value; the check rejects text whose length is zero. This combination allows ordinary nonempty text and rejects ''. [S1]

Here are illustrative outcomes:

1. NULL — rejected by NOT NULL.
2. '' — rejected because its length is zero.
3. 'draft' — accepted because its length is greater than zero.

This is a length rule, not a rule about whether the text looks meaningful. A string containing spaces has characters, so this check does not express “must contain non-space text.”

If you mean ordinary spaces at the beginning or end of the text, check the trimmed value:

CREATE TABLE notes (
  label TEXT NOT NULL CHECK (length(trim(label)) > 0)
);

With SQLite’s default behavior, trim() removes ordinary spaces from both ends. Thus the check rejects an empty string and a string made only of ordinary spaces, while allowing text such as ' draft '. [S2] This behavior should not be described as removing every possible whitespace character. Decide which characters your input rules should treat as whitespace, then choose a rule for that definition.

Assuming the intended rule concerns ordinary spaces, the outcomes are:

1. NULL — rejected by NOT NULL.
2. '' — rejected by the check.
3. ' ' — rejected after trimming.
4. ' draft ' — accepted because text remains after trimming.

Use the version that matches your intended meaning:

-- Empty text is allowed; NULL is not.
CREATE TABLE notes (
  label TEXT NOT NULL
);

-- Text of nonzero length is required; NULL and '' are rejected.
CREATE TABLE notes_nonempty (
  label TEXT NOT NULL CHECK (length(label) > 0)
);

-- Text remaining after trimming ordinary spaces is required.
CREATE TABLE notes_nonspace (
  label TEXT NOT NULL CHECK (length(trim(label)) > 0)
);

These are alternatives, each defining its own table. Before adopting one, write down whether '' should pass and whether input containing only ordinary spaces should pass. Then compare those answers with the examples above. If your requirement includes tabs or other whitespace characters, the behavior described here for default trim() does not settle that broader rule; specify the exact characters you intend to handle and verify an expression for them. [S1] [S2]