In production environment databases, it is often seen that some SQL where conditions include:equal condition on a normal index + primary key range query + order by limitAlthough using a normal index would be more efficient, the system chooses to use index merge instead in some cases. This article explores such index merge situations.Index Merge Official Introduction  The Index Merge access method retrieves rows with multiple range scans and merges their results into one.Generally, for a single table, the optimizer chooses one index. However, in the case of index merge, the optimizer ...