Add the EXISTS Operator for Select Where Filters #572
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VinaiRachakonda
changed the title
zachmu
approved these changes
Sep 28, 2021
| @@ -5284,6 +5284,34 @@ var QueryTests = []QueryTest{ | |||
| {time.Date(2020, 1, 1, 16, 0, 0, 0, time.UTC)}, | |||
| }, | |||
| }, | |||
| { | |||
| Query: `SELECT 1 from dual WHERE EXISTS (SELECT 1 from dual);`, | |||
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Need a test of the EXISTS expression not in the filter
i.e. SELECT EXISTS (SELECT NULL from dual);
sql/plan/existssubquery.go
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| "github.com/dolthub/go-mysql-server/sql/expression" | ||
| ) | ||
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| // ExistsSubquery is an expression that checks that a subquery returns a non emptyset result. It's in the plan package, |
sql/plan/existssubquery.go
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| return nil, fmt.Errorf("error: exists operator should only work with a subquery") | ||
| } | ||
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| results, err := subquery.HashMultiple(ctx, row) |
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Oh nice, I forgot about this method, good use of it
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For some queries this is going to be really inefficient, would be better to check for only a single row, then close the subquery iterator
You should do this as a followup, write a HasResultRow method on Subquery and use that
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Adds the exists operator as described here: https://dev.mysql.com/doc/refman/8.0/en/exists-and-not-exists-subqueries.html