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In the following test case:
drop table if exists t1, t2, t3;
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create table t1 (id int, key (id));
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insert t1 values (1),(2);
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create table t2 (t1_id int primary key, id int, key (id));
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insert t2 values (1,1),(2,2);
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create table t3 (t2_id int primary key);
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insert t3 values (1),(2);
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set sql_quote_show_create=0;
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explain extended select t1.id from t1 left join
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t2 on t1.id = t2.t1_id left join t3 on t2.id = t3.t2_id;
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the optimizer is supposed to eliminate both t2 and t3 from the query plan, but it only removes t3.
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