Subqueries in SET condition of UPDATE statement in presence of foreign keys #15163
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Signed-off-by: Manan Gupta <manan@planetscale.com>
Signed-off-by: Manan Gupta <manan@planetscale.com>
GuptaManan100
added
Type: Enhancement
GuptaManan100
requested review from
harshit-gangal,
systay,
frouioui and
arthurschreiber
as code owners
Review ChecklistHello reviewers! 👋 Please follow this checklist when reviewing this Pull Request. General
Tests
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #15163 +/- ##
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+ Coverage 70.60% 70.63% +0.02%
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Files 1376 1377 +1
Lines 182302 182800 +498
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+ Hits 128721 129123 +402
- Misses 53581 53677 +96 ☔ View full report in Codecov by Sentry. |
systay
approved these changes
Feb 7, 2024
Comment on lines
+132
to
+141
| // updClone is used in foreign key planning to create the selection statements to be used for verification and selection. | ||
| // If we encounter subqueries, we want to fix the updClone to use the replaced expression, so that the pulled out subquery's | ||
| // result is used everywhere instead of running the subquery multiple times, which is wasteful. | ||
| updClone := sqlparser.CloneRefOfUpdate(updStmt) | ||
| for idx, updExpr := range updStmt.Exprs { | ||
| expr, subqs := sqc.pullOutValueSubqueries(ctx, updExpr.Expr, qt.ID, true) | ||
| if len(subqs) == 0 { | ||
| expr = updExpr.Expr | ||
| } else { | ||
| updClone.Exprs[idx].Expr = sqlparser.CloneExpr(expr) |
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what about the case when the subquery gets merged with the outer query?
can we have a test for that as well?
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We can't merge the subquery with the outer query any more. Because the subquery result has to be shared by the select and the update queries, we cannot run the subquery twice, for the reason that it might return different results.
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Is this ensured that the subquery is not merged with the outer?
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subquery is only merged with outer, if the outer is a Join or a Route. For foreign key planning, it will always either be a FkCascade or FkVerify, so it will never merge it. The merging logic is in pushOrMerge in subquery_planning.
harshit-gangal
approved these changes
Feb 8, 2024
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Description
This PR adds the support requested in #15162.
With the changes in this PR, we support having a subquery in a SET clause of an UPDATE statement even if the column is related by foreign keys.
The changes proposed in the PR, are to use a modified clone statement of
UPDATEstatement for foreign key planning that has the subquery replaced by an argument, and to do the foreign key planning underneath the subquery containers so that the inner subqueries run first and their results can be used for the remainder of the update planning.Related Issue(s)
Checklist
Deployment Notes