Query for scopes in MySQL composite index

Create a table:

CREATE TABLE ' Ygzt_test ' (
' ID ' bigint (unsigned) not NULL auto_increment,
' A ' int (one) is not NULL,
' B ' int (one) is not NULL,
' C ' int (one) is not NULL,
' d ' int (one) is not NULL,
PRIMARY KEY (' id '),
KEY ' A ' (' A ', ' B ', ' C ', ' d ')
) Engine=innodb DEFAULT Charset=utf8 collate=utf8_unicode_ci comment= ' test ';

1.Experiment one, no ORDER by

First Add federated Index A,b,c,d

Explain select * from Ygzt_test where a=1 and b=2 and C=3 and d=4

Modify SQL:

Explain select * from Ygzt_test where a>1 and b=2 and C=3 and d=4

Type has been downgraded from ref to index

Modify Index B,c,d,a

Explain select * from Ygzt_test where a>1 and b=2 and C=3 and d=4

Done

2.Experiment two, order by

Building an index, a, b

Explain select * from Ygzt_test where a>0 order by B

As you can see, A>0 uses an index, and order by B is not used

Modify Index to B,a

Explain select * from Ygzt_test where a>0 order by B

Where and order by are not indexed

Thinking of the previous order By+select *

This question is taken out alone in practice:

Modify Index to a

Explain select * FROM Ygzt_test ORDER by a

Explain select * FROM Ygzt_test Force INDEX (a) order by a

Conclusion:

1.--<,<=,=,>,>=,between,like (right blur) applicable index in single-column index

2. The scope of the index, the order of failure, the solution is subject to actual

Query for scopes in MySQL composite index