## Can I omit the second “is” in “is… and is…”?

3

What is the correct syntax:

This column is a primary key and null.

or

This column is a primary key and is null.

Should I write is again?

If you want to skip the second 'is', reverse the clauses. "Null" is a special noun that doesn't take any article, and it makes it look odd in many constructs, where it lacks other words that would make it seem like a normal noun. OTOH 'a primary key' is perfectly clear. So, 'this column is null and a primary key' doesn't make the 'null' seem a weirdly dangling thingy at the end, while 'a primary key' stands on its own just fine. – SF. – 2013-09-11T09:10:44.313

It does seem to walk and quack a lot like an adjective, though. – snailplane – 2013-09-11T10:13:00.540

@Gilles This doesn't have to be analyzed as ellipsis. – snailplane – 2013-09-11T23:17:40.463

@snailboat True, but as mcalex explains, if it isn't, it's a zeugma, and one that I find quite jarring. – Gilles 'SO- stop being evil' – 2013-09-11T23:19:59.437

@Gilles I don't agree with SF's comment or mcalex's answer at all. In any case, I consider the first option ungrammatical, but some other native speakers I asked think it's fine, and some agreed with SF's answer that it's better when you swap the conjuncts. I'm really interested in the wide range of acceptability judgments I got, but I can't explain them terribly well, so I decided not to post my answer... – snailplane – 2013-09-11T23:23:08.240

1@snailboat Mind that the people you ask understand the technical meaning, as it can look ok otherwise. “The column is a primary key” refers to the column in the table. “The column is null” refers a value in that column in a particular row (i.e. it's one cell). – Gilles 'SO- stop being evil' – 2013-09-11T23:26:07.610

@Gilles That's a good point, but in my informal survey, I can find examples of people who understand the meaning but fall on both ends of the acceptability spectrum. So that may be an additional confounding factor, but it doesn't explain whether it's acceptable. – snailplane – 2013-09-12T02:55:31.967

3

I would select 'is null' for both English and SQL reasons.

The alternatives are different in nature. I.e., primary key is singular ('a' primary key), but the null attribute is a mass noun. Having 'is' in front of both alternatives helps to highlight this difference.

Additionally, in SQL the syntax used to query a null column is (eg:)

WHERE column_value *IS NULL*


Because of this construct in the language, it will help to identify that you mean 'null' in an SQL sense (ie, has no data) and not necessarily in an English sense - which could mean invalid or wrong.

4

Special considerations for 'null' aside, to answer your larger English question, the answer is that you don't need a second is. Think of similar constructs:

• The car is red and broken down.
• This column is an example of Ionic architecture and made of pure marble.
• The joke is a very long one, but funny.

In all three cases, we could add another is:

• The car is red and is broken down.
• This column is an example of Ionic architecture and is made of pure marble.
• The joke is a very long one, but it's funny.

In the end, you need to examine the sentence, and see if it reads better with or without the repeated verb. When it's simply two adjectives, it's probably best to leave it out:

• The floor is clean and brand new.

But, when the sentence structure gets more complex, it may be best to add it, for the sake of readability:

• His uncle is a very grumpy executive and is usually late for meetings.

Of course, you can always break that into two sentences, too:

• His uncle is a very grumpy executive. He usually arrives late for meetings.

In short, in the "is... and is...." construct, you can use the verb is once in the same sentence, twice in the same sentence, or break the sentence into two sentences. All are valid options and have their place.