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Multi-table UPDATE/DELETE do not produce a trace at the moment. They should. I am not sure if there is anything specific to be added to the trace about them, just enabling the tracing so that one can see the optimization of their underlying join is good.
create table ten(a int);
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insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
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create table t10 (a int, b int);
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insert into t10 select a,a from ten;
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alter table t10 add key(a);
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create table t11 like t10;
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insert into t11 select * from t10;
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explain delete t10,t11 from t10, t11 where t10.a=t11.a and t11.a<3;
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select * from information_schema.optimizer_trace\G
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