sql/opt: handle non-unique parent for RBR region inference#171056
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When a REGIONAL BY ROW child sets infer_rbr_region_col_using_constraint, the optimizer plans a lookup join into the parent on the FK's non-region columns to infer the region. If those columns aren't a lax key on the parent, the join could return multiple rows per child input row, which tripped an assertion failure in mutation_builder. Allow this configuration: wrap the LeftJoin in an unordered DistinctOn grouped by the child input's key (added via EnsureKey when needed), selecting an arbitrary matching parent row via FirstAgg on the parent's region column. Also moves EnsureKey from decorrelate_funcs.go to general_funcs.go so it can be shared with optbuilder. Fixes cockroachdb#170768 Release note (bug fix): Fixed an internal error that could occur during INSERT/UPDATE/UPSERT on a REGIONAL BY ROW table configured with the infer_rbr_region_col_using_constraint storage parameter when the referenced parent table did not have a unique constraint covering the foreign key's non-region columns. The optimizer now picks an arbitrary matching parent row to infer the region from.
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When a REGIONAL BY ROW child sets infer_rbr_region_col_using_constraint, the optimizer plans a lookup join into the parent on the FK's non-region columns to infer the region. If those columns aren't a lax key on the parent, the join could return multiple rows per child input row, which tripped an assertion failure in mutation_builder.
Allow this configuration: wrap the LeftJoin in an unordered DistinctOn grouped by the child input's key (added via EnsureKey when needed), selecting an arbitrary matching parent row via FirstAgg on the parent's region column.
Also moves EnsureKey from decorrelate_funcs.go to general_funcs.go so it can be shared with optbuilder.
Fixes #170768
Release note (bug fix): Fixed an internal error that could occur during INSERT/UPDATE/UPSERT on a REGIONAL BY ROW table configured with the infer_rbr_region_col_using_constraint storage parameter when the referenced parent table did not have a unique constraint covering the foreign key's non-region columns. The optimizer now picks an arbitrary matching parent row to infer the region from.