When you drop an index, you are dropping a logical index; however, you are not always dropping the physical index to which it refers. If another logical index refers to the same physical index, the physical index is not deleted. This is important to know, especially if you expect disk space to be freed by dropping the index, or if you are dropping the index with the intent to physically recreate it.
To determine whether an index for a table is sharing a physical index with any other indexes, select the table in Sybase Central, and then click the Indexes tab. Note whether the Phys. ID value for the index is also present for other indexes in the list. Matching Phys. ID values mean that those indexes share the same physical index. To recreate a physical index, you can use the ALTER INDEX...REBUILD statement. Alternatively, you can drop all the indexes, and then recreate them.
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