Questions tagged [covering-index]
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16 questions
0 votes
1 answer
65 views
MySQL: How to optimize a JOIN on a primary key with Indexes
I am looking to optimize a JOIN between tables that uses a small subset of columns in the second table. CREATE TABLE `employees` ( `employee_id` bigint NOT NULL, `manager_id` bigint NOT NULL, `...
5 votes
4 answers
893 views
MySQL using a multi-column index even when the first column isn't being queried
I have MySQL version 8.0.37. From what I understand about a multi-column index in this version, it will be used by MySQL ONLY if the query contains a subset of all the columns, starting from the first....
- 203
0 votes
1 answer
830 views
Adding a non-clustered, covering index, on a primary key, when clustered index exists
I went through the related articles, suggested by SO, but didn't really find all the answers, so I'll try to be specific here. Presume we have a (MSSQL) table, with a simple ID (int) primary key, with ...
- 147
2 votes
2 answers
3k views
Non-clustered Primary Key and Clustered Index
It is my understanding that in SQL Server, you can have a Primary Key that is non-clustered, and have another index that is the clustered one. To me, this seems the same as just having a Primary Key, ...
- 829
2 votes
1 answer
238 views
Key lookup still happening after creating covering index
I've implemented a covering index to avoid a key lookup: CREATE INDEX IX_StatusHistory_Covering ON StatusHistory(ID) INCLUDE (Status_ID, StatusComment, StatusReason_ID, ...
- 33
0 votes
2 answers
99 views
non clustered index coverage with INCLUDED columns
If I have two indexes: IDX_1 = (COL1), (COL2) DESC IDX_2 = (COL1) INCLUDE (COL3) will a single defined below cover both queries? does the Descending keyword have any bearing on the usage of INCLUDE ...
- 2,591
0 votes
1 answer
1k views
Column as an Included column or as a key column
I have a query which has an optional where condition on column classID(not unique). This same classID is being displayed as a select column in various other queries. Currently i have classID as an ...
- 1,345
0 votes
1 answer
101 views
Why a query is not covered when using a range operator on documents?
I have created the following 1000 documents: for(i=0;i<1000;i++){db.doc.insert({"doc":{"k1":"v_"+i,"k2":i},"scal":i})} So a document looks like this: var d1 = db.doc.findOne() { "_id" : ...
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