Commits on May 10, 2019

1. sql/analyzer: refactor and fix bugs in qualify_columns rule …

   qualify_columns rule has been a source of bugs for quite a long time
   due to the way we used to look for columns. Before, we looked for
   all available schemas in all the tree of a query (excluding subqueries).
   This required a lot of exceptions and treatments for special cases
   that have been added over time in order to patch the bugs that kept
   appearing.
   It had special cases for aliases, for GroupBy, etc that kept complicating
   the code and making the rule harder to follow and confusing.
   
   This refactor simplifies the logic of the rule and treats all nodes
   in the exact same way so it's simpler, more obvious and easier to
   reason about.
   Now, a node only has knowledge of the columns (aliases or not) defined
   until it reaches the first Project, GroupBy, ResolvedTable or subquery
   in each branch of the tree. This way, we can gather all the available
   columns and infer the schema (which we cannot just call using the Schema
   method because the tree is not resolved yet). Then, qualifying columns
   becomes a trivial job once you have the schema.
   
   All the tests of go-mysql-server and gitbase pass with this new
   implementation of the rule.
   
   Signed-off-by: Miguel Molina <miguel@erizocosmi.co>

   

   erizocosmico committed May 10, 2019
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