The SQL parser as it stands right now ignores alias for aggregate
result, e.g. `SELECT COUNT(*) AS thing FROM s3object` doesn't actually
return record like `{"thing": 42}`, it returns a record like `{"_1": 42}`.
Column alias for aggregate result is supported in AWS's S3 Select, so
this commit fixes that by respecting the `expr.As` in the expression.
Also improve test for S3 select
On top of testing a simple `SELECT` query, we want to test a few more
"advanced" queries (e.g. aggregation).
Convert existing tests into table driven tests[1], and add the new test
cases with "advanced" queries into them.
[1] - https://github.com/golang/go/wiki/TableDrivenTests
This change adds support for casting strings to Timestamp via CAST:
`CAST('2010T' AS TIMESTAMP)`
It also implements the following date-time functions:
- UTCNOW()
- DATE_ADD()
- DATE_DIFF()
- EXTRACT()
For values passed to these functions, date-types are automatically
inferred.
- New parser written from scratch, allows easier and complete parsing
of the full S3 Select SQL syntax. Parser definition is directly
provided by the AST defined for the SQL grammar.
- Bring support to parse and interpret SQL involving JSON path
expressions; evaluation of JSON path expressions will be
subsequently added.
- Bring automatic type inference and conversion for untyped
values (e.g. CSV data).
