[IMPALA-8945] Impala Doc: Incorrect Claim of Equivalence in Impala Docs

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 3.4.0
• Component/s: Docs
• Epic Color: ghx-label-4
• Assignee: Alexandra Rodoni
• Reporter: Alexandra Rodoni
• Created: 14/Sep/19 01:45
• Updated: 17/Sep/19 17:53
• Resolved: 16/Sep/19 21:03

Description

Reported by icook

The Impala docs entry for the IS DISTINCT FROM operator states:

The <=> operator, used like an equality operator in a join query, is more efficient than the equivalent clause: A = B OR (A IS NULL AND B IS NULL). The <=> operator can use a hash join, while the OR expression cannot.

But this expression is not equivalent to A <=> B. See the attached screenshot demonstrating their non-equivalence. An expression that is equivalent to A <=> B is this:

(A IS NULL AND B IS NULL) OR ((A IS NOT NULL AND B IS NOT NULL) AND (A = B))

This expression should replace the existing incorrect expression.

Another expression that is equivalent to A <=> B is:

if(A IS NULL OR B IS NULL, A IS NULL AND B IS NULL, A = B)

This one is a bit easier to follow. If you use this one in the docs, just replace the following line with:

The <=> operator can use a hash join, while the if expression cannot.