Aren't blank and NULL the same thing?

Not in Postgres, MySQL, or SQL Server. NULL means unknown / no value. '' is a real string of length zero. IS NULL does not match ''. A signup form that writes '' for a skipped field is invisible to a NULL-only count.

I thought Oracle treated '' as NULL?

Oracle does collapse empty strings to NULL. That habit leaks into prompts and training data. It is not how Postgres or SQL Server work, and MySQL stores '' as ''.

Should I use IS NULL OR = '' every time?

When the question is 'missing / not filled in,' yes — or normalize with NULLIF(email, '') IS NULL, which treats both as missing. Don't do it for a column that legitimately uses '' as a coded value.

Is this the same as COUNT(email) skipping NULLs?

Related family. COUNT(email) skips NULL and still counts ''. IS NULL skips '' and still misses those rows. Both under-count 'how many have no real email,' from opposite sides.

What about whitespace-only emails?

TRIM(email) = '' catches ' '. That's a third bucket. If you're cleaning a count of 'no usable email,' check NULL, '', and trim-empty.

Empty String vs NULL SQL | Blank Field Count

You ask "how many customers have no email?" The AI writes WHERE email IS NULL and returns 140. You know hundreds of people signed up without typing one. The form stored '', not NULL. Those rows are not missing to SQL — they have a value. It's just empty.

`''` is a value

WHERE email IS NULL          -- 140 rows
WHERE email = ''             -- 610 rows
WHERE email IS NULL OR email = ''   -- 750 rows

Three different answers to what sounded like one question. No error. The first one is what models reach for because "no email" maps cleanly onto NULL in textbooks — and because Oracle treats '' as NULL, a habit that does not apply to Postgres, MySQL, or SQL Server.

This sits next to IS NULL dropping rows from != filters and COUNT(column) skipping NULLs. Those are about NULL's three-valued logic. This one is about the other missing: a present, empty string the UI still shows as blank.

How to catch it

Ask for the split, not one number:

How many customers have email IS NULL?
How many have email = ''?
How many have TRIM(email) = ''?
Show all three and the SQL.

If the second or third is non-zero, a NULL-only "missing" count is incomplete. Same check for name, phone, notes, plan — any field a form can submit empty.

One-liner that treats both as missing:

WHERE NULLIF(TRIM(email), '') IS NULL

NULLIF(x, '') turns '' into NULL; TRIM folds whitespace-only into the same bucket.

The prompt that heads this off

When I ask for missing / blank / no X, don't use IS NULL alone.
Check describe_table, then count NULL, '', and TRIM(column) = ''
separately unless I say the column is never empty-string.
Prefer NULLIF(TRIM(column), '') IS NULL for "no usable value."

The short version

Blank in the admin UI is not one SQL thing. NULL and '' are different rows. If the "no email" count looks low, you probably only counted the first.

Read-only MCP gateway: mcpserver.design.

Related reading:

'' is a value

How to catch it

The prompt that heads this off

The short version

`''` is a value