Oracle hint, oraclehint

Oracle hint, oraclehint

1. use_concat

Online statement:

The CONCATENATION and UNION/union all operations are similar. According to the OR query condition, a query is divided into two OR more parts, and the duplicate records are removed. Since the CONCATENATION execution plan needs to remove duplicate records, it is different from union all. Unlike UNION, this execution plan does not remove all duplicate records, but filters out records that are repeated between two subqueries. In 10 Gb, the execution plan and prompt are reserved for backward compatibility. We can see that by default, the COST of the CONCATENATION execution plan is lower, oracle does not select such an execution plan;

If use_concat is invalid for or subqueries, try/* + use_concat (or_predicates (1 ))*/

Opposite to use_concat, no_expand