index join
The index join node is used to access column data where the column is referred to in the query but does not have a covering index.
Detailed Description
The index join node is used to access column data where the column is referred to in the query but does not have a covering index.
For example a table has three columns, colA, colB and colC with a primary key on colA and colB.
SELECT colC FROM table WHERE colA = 10 and colB = 1;
Because the unindexed column is being retrieved, a lookup on the primary key is required to access the value in colC. This lookup is called an index join and can be costly. Using a STORING clause for colC on the index can ensure the index ‘covers’ all the data queried and make the additional index lookup unnecessary.
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