mysql查询没有使用我想要的索引

Question

我有以下查询左连接 2 个表:

explain 

    select 
        n.* from npi n left join npi_taxonomy nt on n.NPI=nt.NPI_CODE 

    where 
        n.Provider_First_Name like '%s%' and 
        n.Provider_Last_Name like '%b%' and 
        n.Provider_Business_Practice_Location_Address_State_Name = 'SC' and 
        n.Provider_Business_Practice_Location_Address_City_Name = 'charleston' and 
        n.Provider_Business_Practice_Location_Address_Postal_Code in (29001,29003,29010,29016,29018,29020,29030,29032,29033,29038,29039,29040,29041,29042,29044,29045,29046,29047,29048,29051,29052,29053,29056,29059,29061,29062,29069,29071,29072,29073,29078,29079,29080,29081,29082,29102,29104,29107,29111,29112,29113,29114,29115,29116,29117,29118,29123,29125,29128,29133,29135,29137,29142,29143,29146,29147,29148,29150,29151,29152,29153,29154,29160,29161,29162,29163,29164,29168,29169,29170,29171,29172,29201,29202,29203,29204,29205,29206,29207,29208,29209,29210,29212,29214,29215,29216,29217,29218,29219,29220,29221,29222,29223,29224,29225,29226,29227,29228,29229,29230,29240,29250,29260,29290,29292,29401,29402,29403,29404,29405,29406,29407,29409) and 
        n.Entity_Type_Code = 1 and 
        nt.Healthcare_Provider_Taxonomy_Code in ('101Y00000X') 

    limit 0,10; 

我添加了一个多列索引:

npi_fname_lname_state_city_zip_entity 在表 npi 上，它按以下顺序对列进行索引:

NPI,  
Provider_First_Name, 
Provider_First_Name, 
Provider_Business_Practice_Location_Address_State_Name, Provider_Business_Practice_Location_Address_City_Name, Provider_Business_Practice_Location_Address_Postal_Code, 
Entity_Type_Code

但是，当我对查询进行解释时，它告诉我它使用主索引 (NPI)。此外，它说已检查的行数 = 1

更糟糕的是:查询大约需要 120 秒来执行。我该如何优化它？

在此方面，我非常感谢您的帮助。

Answer 1

您的多列索引没有帮助的原因是您使用通配符如“%s%” 进行过滤。

索引只能在使用索引的最左边前缀过滤时使用，这意味着1) cannot do a contains search , 和 2) 如果不能使用多列索引的最左边的列，索引中的其他列 cannot be used aswell .

您应该将索引中列的顺序切换为

Provider_Business_Practice_Location_Address_State_Name, 
Provider_Business_Practice_Location_Address_City_Name, 
Provider_Business_Practice_Location_Address_Postal_Code, 
Entity_Type_Code

这样 MySql 将只扫描符合这些列(SC、charleston 等)条件的行。

或者，查看 full text indexes .