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28 lines
1.2 KiB
Plaintext
28 lines
1.2 KiB
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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CREATE TABLE t1(a int, b int, KEY (a), PRIMARY KEY (b)) ENGINE=InnoDB;
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CREATE TABLE t2 (b int, PRIMARY KEY (b));
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INSERT INTO t2 VALUES (4),(9);
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SELECT STRAIGHT_JOIN t1.a FROM t1 RIGHT JOIN t2 ON t1.b = t2.b
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WHERE (t1.b NOT BETWEEN 1 AND 7 OR t1.a IS NULL AND t1.b = t2.b) AND t2.b = 4
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GROUP BY 1;
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a
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DROP TABLE t1,t2;
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