I have a table with 1 million records out of which 10,000 records are of unique records, then if I will implement index, then which type of index shall I use and why shall I use?
Answers were Sorted based on User's Feedback
Answer / thanjairajan@gmail.com
You Can use Bitmap Index. Because while no.of unique record is small than no.of total record, we can use bitmap index. i.e we can use bitmap index in low cardinality column.
For example a table contain name,address,sex column. in sex column may be two values. i.e male and female. so this distinct values small but no.of total records is high.
So in this situation we can use bitmap index.
Is This Answer Correct ? | 9 Yes | 0 No |
Answer / mrityunjay singh
Fully indexing a large table with a traditional B-tree index can be prohibitively expensive in terms of disk space because the indexes can be several times larger than the data in the table. Bitmap indexes are typically only a fraction of the size of the indexed data in the table.
An index provides pointers to the rows in a table that contain a given key value. A regular index stores a list of rowids for each key corresponding to the rows with that key value. In a bitmap index, a bitmap for each key value replaces a list of rowids.
Each bit in the bitmap corresponds to a possible rowid, and if the bit is set, it means that the row with the corresponding rowid contains the key value. A mapping function converts the bit position to an actual rowid, so that the bitmap index provides the same functionality as a regular index. Bitmap indexes store the bitmaps in a compressed way. If the number of distinct key values is small, bitmap indexes compress better and the space saving benefit compared to a B-tree index becomes even better.
Is This Answer Correct ? | 0 Yes | 0 No |
how can we encrypt and decrypt a data present in a mysql table using mysql? : Sql dba
have table with two columns with datatypes as number and varchar and the values in A column like 1,2,3 AND B column values like a,b,c. now need to display data in a single column as 1,a,2,b,3,c.
Write a query to find five highest salaries from EMP table. (there is a column SALARY)
24 Answers Cap Gemini, iNautix,
what is Difference between Having and Where clause?
Advantages and disadvantages of stored procedure?
What is pl sql block in dbms?
How do you get column names only for a table (sql server)?
What plvcmt and plvrb does in pl/sql?
What is recursive join in sql?
suppose we have values like 1 5 7 in a colum.Now we want numbers like(2 3 4 6) that exists between 1 5 7.How can we do this using sql query??
what are numeric data types? : Sql dba
Explain what is sql?