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# Bug#12540545 61101: ASSERTION FAILURE IN THREAD 1256741184 IN
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# FILE /BUILDDIR/BUILD/BUILD/MYSQ
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CREATE TABLE t1 (a CHAR(1), b CHAR(1), PRIMARY KEY (a,b)) ENGINE=InnoDB;
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INSERT INTO t1 VALUES ('a', 'b'), ('c', 'd');
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EXPLAIN SELECT COUNT(DISTINCT a) FROM t1 WHERE b = 'b';
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index NULL PRIMARY 2 NULL 2 Using where; Using index
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SELECT COUNT(DISTINCT a) FROM t1 WHERE b = 'b';
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CREATE TABLE t1 (a CHAR(1) NOT NULL, b CHAR(1) NOT NULL, UNIQUE KEY (a,b))
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INSERT INTO t1 VALUES ('a', 'b'), ('c', 'd');
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EXPLAIN SELECT COUNT(DISTINCT a) FROM t1 WHERE b = 'b';
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index NULL a 2 NULL 2 Using where; Using index
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SELECT COUNT(DISTINCT a) FROM t1 WHERE b = 'b';