[SPARK-27912] Improve parser error message for CASE clause

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.1.0
• Component/s: SQL
• Assignee: Unassigned
• Reporter: Yesheng Ma
• Created: 31/May/19 21:32
• Updated: 29/Mar/20 02:33

Description

The CASE clause is commonly used in SQL queries, but people can forget the trailing END. When a user queries such a statement, the error message is confusing. For example, the error message for

SELECT (CASE WHEN a THEN b ELSE c) FROM a;

is

no viable alternative at input '(CASE WHEN a THEN b ELSE c)'(line 1, pos 33)

which is misleading.
 

One possible way to fix is to explicitly capture these statements in a grammar rule and print user-friendly error message such as

missing trailing END for case clause