1
CREATE TABLE t1 (t1i int);
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CREATE TABLE t2 (t2i int);
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CREATE TABLE t3 (t3i int);
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CREATE TABLE t4 (t4i int);
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INSERT INTO t1 VALUES (1);
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INSERT INTO t2 VALUES (1),(2);
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INSERT INTO t3 VALUES (1),(2);
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INSERT INTO t4 VALUES (1),(2);
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FROM t1 JOIN t4 ON t1i=t4i
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 ALL NULL NULL NULL NULL 1 Using where
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1 PRIMARY t4 ALL NULL NULL NULL NULL 2 Using where; Using join buffer
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2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
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3 SUBQUERY t3 ALL NULL NULL NULL NULL 2 Using temporary; Using filesort
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DROP TABLE t1,t2,t3,t4;