Avoiding the Full-Table Scan
A full-table scan occurs when the database server reads every record in a table in order to execute a SQL statement. Full-table scans are normally an issue when dealing with queries or the SELECT statement. However, a full-table scan can also come into play when dealing with updates and deletes. A full-table scan occurs when the columns in the WHERE clause do not have an index associated with them. A full-table scan is like reading a book from cover to cover and trying to find a keyword. Most often, you will opt to use the index.
You can avoid a full-table scan by creating an index on columns that are used as conditions in the WHERE clause of a SQL statement. Indexes provide a direct path to the data the same way ...
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