1. Overlay index: The "Nonclustered index column" should exist in the result set contained in select and where, so that the index table can be done without looking up the base table; 2. Index Cross: is for an extension of the overlay index (here the nonclustered index is built in L1 and L2, select * from t _ Where l1= ' asd ' and l2= ' qwe '), then two nonclustered index tables are join;3. Index Connection: is a special case of index crossover (select L1,l2 from T_ where l1= ' ASD ' and l2= ' qwe '); 4. Cable Filter: When the index is created with a specific filter conditions, then this condition will not be; NOTE:
Create nonclustered index AAA on [111].[ DBO]. [Sys_message] ([Type],[subject]) include ([status]) include contains not as the width of the Add "key" create nonclustered index CCC on [111].[ DBO]. [Sys_message] ([Subject])
Examples of index filtering are as follows:
Create nonclustered index AAA on [111].[ DBO]. [Sys_message] ([Type],[subject]) where [subject]=0
SQL Server non-clustered index overrides, joins, crosses, filters
