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Use a self-join for UPDATE with outer joins #1323

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Apr 3, 2025
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Use a self-join for UPDATE with outer joins #1323

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Use a self-join for UPDATE with outer joins
aidanharan Apr 3, 2025
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aidanharan Apr 3, 2025
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54 changes: 17 additions & 37 deletions lib/arel/visitors/sqlserver.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -42,57 +42,37 @@ def visit_Arel_Nodes_UpdateStatement(o, collector)
#
# UPDATE t1
# SET ..
# FROM t2
# WHERE t1.join_id = t2.join_id
#
# Or if more than one join is present:
#
# UPDATE t1
# SET ..
# FROM t2
# JOIN t3 ON t2.join_id = t3.join_id
# WHERE t1.join_id = t2.join_id
# FROM t1 JOIN t2 ON t2.join_id = t1.join_id ..
# WHERE ..
if has_join_sources?(o)
visit o.relation.left, collector
collector = visit o.relation.left, collector
collect_nodes_for o.values, collector, " SET "
collector << " FROM "
first_join, *remaining_joins = o.relation.right
from_items = remaining_joins.extract! do |join|
join.right.expr.right.relation == o.relation.left
end

from_where = [first_join.left] + from_items.map(&:left)
collect_nodes_for from_where, collector, " ", ", "

if remaining_joins && !remaining_joins.empty?
collector << " "
remaining_joins.each do |join|
visit join, collector
collector << " "
end
end

from_where = [first_join.right.expr] + from_items.map { |i| i.right.expr }
collect_nodes_for from_where + o.wheres, collector, " WHERE ", " AND "
collector = inject_join o.relation.right, collector, " "
else
collector = visit o.relation, collector
collect_nodes_for o.values, collector, " SET "
collect_nodes_for o.wheres, collector, " WHERE ", " AND "
end

collect_nodes_for o.wheres, collector, " WHERE ", " AND "
collect_nodes_for o.orders, collector, " ORDER BY "
maybe_visit o.limit, collector
end

# Same as PostgreSQL and SQLite except we need to add limit if using subquery.
# Similar to PostgreSQL and SQLite.
def prepare_update_statement(o)
if has_join_sources?(o) && !has_limit_or_offset_or_orders?(o) && !has_group_by_and_having?(o) &&
# The dialect isn't flexible enough to allow anything other than a inner join
# for the first join:
# UPDATE table SET .. FROM joined_table WHERE ...
(o.relation.right.all? { |join| join.is_a?(Arel::Nodes::InnerJoin) || join.right.expr.right.relation != o.relation.left })
o
if o.key && has_join_sources?(o) && !has_group_by_and_having?(o) && !has_limit_or_offset_or_orders?(o)
# Join clauses cannot reference the target table, so alias the
# updated table, place the entire relation in the FROM clause, and
# add a self-join (which requires the primary key)
stmt = o.clone

stmt.relation, stmt.wheres = o.relation.clone, o.wheres.clone
stmt.relation.right = [stmt.relation.left, *stmt.relation.right]
# Don't need to use alias
stmt
else
# If using subquery, we need to add limit
o.limit = Nodes::Limit.new(9_223_372_036_854_775_807) if o.orders.any? && o.limit.nil?

super
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