[IMPALA-5929] Remove useless explicit casts to string

• Type: Bug
• Status: Reopened
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: Impala 2.5.0, Impala 2.6.0, Impala 2.7.0, Impala 2.8.0, Impala 2.9.0, Impala 2.10.0
• Component/s: Frontend
• Epic Color: ghx-label-4
• Assignee: Bikramjeet Vig
• Reporter: Alexander Behm
• Created: 13/Sep/17 18:01
• Updated: 19/Jun/20 18:36

Description

Some BI tools like to generate expressions that look like this:

cast(numeric_col as string) = '123456'

Casting and comparing as string is expensive and we should convert such expressions to:

numeric_col = 123456

Such transformations may be applicable in other situations as well. We should be careful about transforming inequality predicates because the string and numeric comparison might not always be equivalent. For example, the following transformation would be wrong:

cast(numeric_col as string) = '0123456'

is not equivalent to

numeric_col = 123456

Issue Links

• is related to: IMPALA-7960 wrong results when comparing timestamp casted to varchar of smaller length to a string literal in a binary predicate