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20 lines
907 B
Plaintext
20 lines
907 B
Plaintext
CREATE TABLE t1 (id int(11) NOT NULL PRIMARY KEY, name varchar(20),
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INDEX (name)) ENGINE=InnoDB;
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CREATE TABLE t2 (id int(11) NOT NULL PRIMARY KEY, fkey int(11),
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FOREIGN KEY (fkey) REFERENCES t2(id)) ENGINE=InnoDB;
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INSERT INTO t1 VALUES (1,'A1'),(2,'A2'),(3,'B');
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INSERT INTO t2 VALUES (1,1),(2,2),(3,2),(4,3),(5,3);
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EXPLAIN
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SELECT COUNT(*) FROM t2 LEFT JOIN t1 ON t2.fkey = t1.id
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WHERE t1.name LIKE 'A%';
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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 PRIMARY,name name 23 NULL 3 Using where; Using index
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1 SIMPLE t2 ref fkey fkey 5 test.t1.id 1 Using where; Using index
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EXPLAIN
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SELECT COUNT(*) FROM t2 LEFT JOIN t1 ON t2.fkey = t1.id
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WHERE t1.name LIKE 'A%' OR FALSE;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 index NULL fkey 5 NULL 5 Using index
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1 SIMPLE t1 eq_ref PRIMARY PRIMARY 4 test.t2.fkey 1 Using where
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DROP TABLE t1,t2;
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