Oracle performance optimization operation 15: functional-based index requirements equality matching

Oracle performance optimization operation 15: functional-based index requirements equality matching

We have created a function-based index, but if you execute the following query:

<Span style = "font-size: 18px;"> select * from emp where substr (ename, 1, 1) = 's'; </span>

The expected execution plan will still be (table access full), because function-based indexes will take effect only when the data column can match equations,

In this way, the requirements for the planning and maintenance of such indexes are high. Note that adding an index to a table is very dangerous because it will lead to many changes to the query execution plan.

However, if we use a function-based index, this issue will not occur because Oracle uses this type of index only when matching built-in functions are used for queries.