整形數字和字串數字的索引使用情況
阿新 • • 發佈：2019-01-29
http://imysqldba.blog.51cto.com/1222376/1277307
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DROP TABLE ix_test;
CREATE TABLE ix_test
(id_1 varchar(20) NOT NULL,
PRIMARY KEY(id_1));
INSERT INTO ix_test VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11);
|
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mysql>
explain select * from ix_test where id_1=1;
+----+-------------+---------+-------+---------------+---------+---------+------+------+--------------------------+|
id | select_type | table |
type | possible_keys | key |
key_len | ref | rows |
Extra |
+----+-------------+---------+-------+---------------+---------+---------+------+------+--------------------------+
|
1 | SIMPLE | ix_test | index | PRIMARY | PRIMARY|
302 | NULL |
11 | Using where;
Using index |
+----+-------------+---------+-------+---------------+---------+---------+------+------+--------------------------+
1
row in set (0.00
sec)
mysql>
explain select * from ix_test where id_1='1';
+----+-------------+---------+-------+---------------+---------+---------+-------+------+-------------+
|
id | select_type | table |
type | possible_keys | key |
key_len | ref | rows |
Extra |
+----+-------------+---------+-------+---------------+---------+---------+-------+------+-------------+
|
1 | SIMPLE | ix_test | const | PRIMARY | PRIMARY |
302 | const | 1 | Using index |
+----+-------------+---------+-------+---------------+---------+---------+-------+------+-------------+
1
row in set (0.01
sec)
|