Database Interview Questions And Answers |
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28.What is a join and explain different types of joins?
Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS. |
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29.
What is a self join?
Self join is just like any other join, except that two instances of the same table will be joined in the query. |
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30.Define Fact tables and dimension tables?
Fact tables are central tables in data warehousing.They contain the aggregate values that are used in business process. Dimension tables describe the attributes of the fact table.
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31.Explain the ETL process in Data warehousing
Extraction, Transformation and loading are different stages in data warehousing.
Extraction
In this phase, data is extracted from the source and loaded in a structure of data warehouse.
Transformation
After extraction cleaning process happens for better analysis of data.
Loading
After cleaning, data is loaded in the structure of data warehousing. |
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32.
What is Data mining?
Data mining is a process of analyzing current data and summarizing the information in more useful manner. It is useful in analyzing how good business is going and also helps in forecasting business status. |
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33.
What are indexes?
Index can be thought as index of the book that is used for fast retrieval of information.
Index uses one or more column index keys and pointers to the record to locate record.
Index is used to speed up query performance.
Both exist as B-tree structure.
Kind of the indexes are clustered and non-clustered. |
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34.
Explain the types of indexes?
Clustered index
Non-clustered
Clustered index
Clustered index exists as sorted row on disk.
Clustered index re-orders the table record.
Clustered index contains record in the leaf level of the B-tree.
There can be only one Clustered index possible in a table.
Non-clustered
Non-clustered index is the index in which logical order doesn’t match with physical order of stored data on disk.
Non-clustered index contains index key to the table records in the leaf level.
There can be one or more Non-clustered indexes in a table. |
