Writing assignment due on Thursday, November 7

when I searched the information for indexing, the general ideas for index is creating a special sign for each particular record or informations. In mathematic field, index means a number or other symbol that specifies an element of an set.
In computer science field, the index is using for retrieving the the information or the record for people to apply.Moreover, in sql indexes are formed by values in columns.
For creating the index command:

CREATE INDEX index_name
ON table_name (column_name);

under this condition, we have several thing to note:

Indexes should not be used on small tables.

Tables that have frequent, large batch updates or insert operations.

Indexes should not be used on columns that contain a high number of NULL values.

Columns that are frequently manipulated should not be indexed.