Jay Narale created CALCITE-5248:
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Summary: Support Column Aliasing feature in the where clause
Key: CALCITE-5248
URL: https://issues.apache.org/jira/browse/CALCITE-5248
Project: Calcite
Issue Type: New Feature
Reporter: Jay Narale
Based on the discussion
[https://lists.apache.org/thread/7zk5wqgsk64903w5mbt72pwjmsftx0kz].
The goal is to support column aliasing. An example is Teradata /
[https://docs.teradata.com/r/Teradata-Database-SQL-Fundamentals/June-2017/Basic-SQL-Syntax/Referencing-Object-Names-in-a-Request/Using-a-Column-Alias]
A few edge cases to be considered for proper semantics
1. When SubQuery( maybe table) in from and Alias have the same name
eg
SELECT c_customerId as c FROM ( SELECT c FROM table) WHERE c = 'test'
SELECT trim(c_customer_name) as c FROM ( SELECT c FROM table) WHERE c =
'test'
Comments
In a database, the execution order is FROM > WHERE > SELECT so the semantics
should be that column in the subquery is given priority and a filter is
applied to that column
Behavior in Teradata
Consistent with the above, a Filter is applied to the SubQuery
2. When a correlated column outside the query has the same name as the alias
TBD
Here I think the behavior should be identical to the behavior in OrderBy
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