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Can index be duplicate values?
Yes, you can create a clustered index on key columns that contain duplicate values. For example, you might decide to create a clustered index on the LastName column of a table that contains customer data.
Which field Cannot contain duplicate values?
Multi-valued lookup or attachment fields cannot contain duplicate values.
Can we create multiple indexes on table?
It is possible for an index to have two or more columns. Multi column indexes are also known as compound or concatenated indexes. Let us look at a query that could use two different indexes on the table based on the WHERE clause restrictions. We first create these indexes.
Which is the best column to put first in an index?
In general, you should put the column expected to be used most often first in the index. create a composite index putting the most selective column first; that is, the column with the most values.
Why do columns generally make good indexes in MySQL?
The EXPLAIN statement helps you to reveal that how MySQL will execute a query. It shows how and in what order tables are joined. This can be much useful for determining how to write optimized queries, and whether the columns are needed to be indexed. Any index (good/bad) increases insert and update time.
Which is the best data type for index?
For example, the best candidate data type for the SQL Server index is the integer column due to its small size. On the other hand, columns with text, ntext, image, varchar (max), nvarchar (max), and varbinary (max) data types cannot participate in the index key. However, most of it still can be added to the non-clustered non-key columns.
How to arrange columns in a composite index?
One of the arguments for arranging columns in the composite index in order from the least discriminating (less distinct values) to the most discriminating (more distinct values) is for index key compression. SQL> create table t as select * from all_objects; Table created.