Question: While converting some Access queries to T-SQL, I came across the Access function IIf. I read the documentation [here](https://support.microsoft.com/en-us/office/iif-function-32436ecf-c629-48a3-9900-647539c764e3) and understand it takes 3 parameters: the expression, the if true, and the if false. What I have yet to find is if the "false" param is required? And if a false is not provided, what is the behavior?

**UPDATE:**
When this question was asked, I did not ***know*** if the query worked with only 2 parameters (b/c I can not run the query in Access). I did, however, ***suspect it might work*** (with only 2 params) b/c a few queries I am converting (to T-SQL) have nested IIF's and the last IIF has only 2 params.

Answer: 
Addendum to June7's excellent answer:

Here are two simple queries that work in Access SQL:

```
SELECT IIf(1=1, "yes")

```

(returns "yes")

```
SELECT IsNull(IIf(1=2, "yes"))

```

(returns -1 aka True) - so if you omit `falsepart`, `IIf()` returns indeed NULL if `expr` doesn't evaluate to True.
Yes, it's required, it's actually like an if else statement.

i.e an action occurs if the condition is fulfilled, and another action occurs if condition is not fulfilled