MySQL索引长时间运行的查询 - 是否使用密钥？

Question

我正在处理我的数据库（mysql）的大表。我的一些查询运行时间超过5分钟。这里是缓慢的运行我的查询的例子：

select b.DESCRIPTION collateral_type, a.description brand, a.year, 
     a.model, a.plate_number, d.description fuel, a.chassis_number, 
     a.engine_number, c.description as color, insurance_name 
from lms_loan_application_collateral a inner join 
    lms_collateral_type b 
    on a.COLLATERAL_TYPE_ID = b.id left join 
    lms_color c 
    on a.color_id = c.id left join 
    lms_fuel_type d 
    on a.fuel_type_id = d.id inner join 
    lms_loan_application e 
    on e.id = a.loan_application_id inner join 
    lms_dlr_dtl f 
    on e.code = f.lano inner join 
    lms_loanapp_dtl g 
    on f.lano = g.lano 
where b.description in ('Motorcycle', 'Automotive', 'Heavy Equipment'); 

这里的关键是列下的查询

+----+-------------+-------+-------+--------------------------------------------------------+-------------------------+---------+------------+-------+----------------------------------------------------+ 
    | id | select_type | table | type | possible_keys           | key      | key_len | ref  | rows | Extra            | 
    +----+-------------+-------+-------+--------------------------------------------------------+-------------------------+---------+------------+-------+----------------------------------------------------+ 
    | 1 | SIMPLE  | g  | index | lms_loanapp_dtl_lano         | lms_loanapp_dtl_lano | 23  | NULL  | 23432 | Using where; Using index       | 
    | 1 | SIMPLE  | f  | ref | lano             | lano     | 23  | new.g.LANO |  1 | Using index          | 
    | 1 | SIMPLE  | b  | ALL | lms_collateral_type_description,lms_collateral_type_id | NULL     | NULL | NULL  | 11 | Using where; Using join buffer (Block Nested Loop) | 
    | 1 | SIMPLE  | a  | ref | collateral_type_id          | collateral_type_id  | 5  | new.b.ID | 4067 | Using index condition        | 
    | 1 | SIMPLE  | e  | ref | lms_loan_application_id        | lms_loan_application_id | 153  | func  |  1 | Using index condition; Using where     | 
    | 1 | SIMPLE  | c  | ALL | LMS_color_id           | NULL     | NULL | NULL  | 20 | Range checked for each record (index map: 0x1)  | 
    | 1 | SIMPLE  | d  | ALL | LMS_fuel_type_id          | NULL     | NULL | NULL  |  4 | Using where; Using join buffer (Block Nested Loop) | 
    +----+-------------+-------+-------+--------------------------------------------------------+-------------------------+---------+------------+-------+----------------------------------------------------+ 

的mysql的解释，有NULL值。我不确定mysql是否使用我创建的索引键。

下面是我对所涉及的表中创建的索引列表：

SHOW指数从lms_loan_application_collat​​eral从新的;

+---------------------------------+------------+---------------------+--------------+---------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table       | Non_unique | Key_name   | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +---------------------------------+------------+---------------------+--------------+---------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_loan_application_collateral |   1 | color_id   |   1 | color_id   | A   |   36 |  NULL | NULL | YES | BTREE  |   |    | 
    | lms_loan_application_collateral |   1 | fuel_type_id  |   1 | fuel_type_id  | A   |   6 |  NULL | NULL | YES | BTREE  |   |    | 
    | lms_loan_application_collateral |   1 | loan_application_id |   1 | loan_application_id | A   |  89493 |  NULL | NULL | YES | BTREE  |   |    | 
    | lms_loan_application_collateral |   1 | collateral_type_id |   1 | collateral_type_id | A   |   22 |  NULL | NULL | YES | BTREE  |   |    | 
    +---------------------------------+------------+---------------------+--------------+---------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

SHOW指数从lms_collat​​eral_type从新的;

+---------------------+------------+---------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table    | Non_unique | Key_name      | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +---------------------+------------+---------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_collateral_type |   1 | lms_collateral_type_description |   1 | DESCRIPTION | A   |   11 |  NULL | NULL | YES | BTREE  |   |    | 
    | lms_collateral_type |   1 | lms_collateral_type_id   |   1 | ID   | A   |   11 |  NULL | NULL | YES | BTREE  |   |    | 
    +---------------------+------------+---------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

SHOW INDEX FROM lms_color FROM new;

+-----------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table  | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +-----------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_color |   1 | LMS_color_id |   1 | id   | A   |   20 |  NULL | NULL |  | BTREE  |   |    | 
    +-----------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

SHOW INDEX FROM lms_fuel_type FROM new;

+---------------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table   | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +---------------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_fuel_type |   1 | LMS_fuel_type_id |   1 | id   | A   |   4 |  NULL | NULL | YES | BTREE  |   |    | 
    +---------------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

SHOW INDEX FROM lms_loan_application FROM new;

+----------------------+------------+-------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table    | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +----------------------+------------+-------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_loan_application |   1 | lmspis_id    |   1 | PIS_ID  | A   |  1878 |  NULL | NULL | YES | BTREE  |   |    | 
    | lms_loan_application |   1 | loan_type_id   |   1 | LOAN_TYPE_ID | A   |   6 |  NULL | NULL | YES | BTREE  |   |    | 
    | lms_loan_application |   1 | lms_loan_application_id |   1 | ID   | A   |  1878 |  NULL | NULL | YES | BTREE  |   |    | 
    +----------------------+------------+-------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

SHOW INDEX FROM lms_dlr_dtl FROM new;

+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_dlr_dtl |   0 | PRIMARY |   1 | LDDID  | A   |  90066 |  NULL | NULL |  | BTREE  |   |    | 
    | lms_dlr_dtl |   1 | lano  |   1 | LANO  | A   |  90066 |  NULL | NULL | YES | BTREE  |   |    | 
    +-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

SHOW INDEX FROM lms_loanapp_dtl FROM new;

+-----------------+------------+----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | Table   | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
    +-----------------+------------+----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
    | lms_loanapp_dtl |   0 | PRIMARY    |   1 | LLADID  | A   |  23432 |  NULL | NULL |  | BTREE  |   |    | 
    | lms_loanapp_dtl |   1 | lms_loanapp_dtl_lano |   1 | LANO  | A   |  23432 |  NULL | NULL | YES | BTREE  |   |    | 
    +-----------------+------------+----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

Answer 1

指示类型为ALL的表不使用索引。在表上的id列上创建索引代表c和d，以及b上的描述和id列上的一个索引。

create index ix_id on lms_color(id); 
create index ix_id on lms_fuel_type(id); 
create index ix_description_id on lms_collateral_type(description,id); 

Answer 2

由于基数较低，MySQL正在为您的WHERE使用ALL。因此，MySQL认为对11个表项进行表扫描比使用带索引的二进制搜索更便宜。

真正的问题是，您不使用索引具有较高基数的列进行筛选（lms_loanapp_dtl_lano和collateral_type_id）。