vtexplain support select distinct and other expressions #5139
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Rework the vtexplain simulated mysql to handle more expression types when calculating fake column results based on inferences off the select expression. Also change the engine so that it logs an error instead of failing outright, since the column values aren't always needed for it to effectively simulate a query. Signed-off-by: Michael Demmer <mdemmer@slack-corp.com>
Signed-off-by: Michael Demmer <mdemmer@slack-corp.com>
Signed-off-by: Michael Demmer <mdemmer@slack-corp.com>
sougou
approved these changes
Aug 30, 2019
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Summary
Add support for
select distinct,substr,case, and more expressions to vtexplain.Description
Part of the vtexplain execution engine fabricates query results, and so it needs to know the type of each column that should be in the result set.
Rework the analyzer that infers the column type from the select expression so that it handles parenthesized expressions like substr and select distinct(col), as well as case expressions.
Also change the engine so that it logs an error instead of failing outright if it can't resolve an expression to a column type, since the column values aren't always needed for it to effectively simulate a query.