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How SQL Indexes Work internally ?

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When an index is created, it records the location of values in a table that are associated with the column that is indexed. Entries are added to the index when new data is added to the table. When a query is executed against the database and a condition is specified on a column in the WHERE clause that is indexed, the index is first searched for the values specified in the WHERE clause. If the value is found in the index, the index returns the exact location of the searched data in the table. Figure 16.1 illustrates how an index functions. Suppose the following query was issued: SELECT *  FROM TABLE_NAME WHERE NAME = 'SMITH'; As shown in Figure 16.1, the NAME index is referenced to resolve the location of all names equal to 'SMITH'. After the location is determined, the data can be quickly retrieved from the table. The data, in this case names, is alphabetized in the index. A full table scan would occur if there were no index on the table and the same que...
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UML,HLD and LLD.

UML is a standard language for specifying, visualizing, constructing, and documenting the artifacts of software systems. Here is a Complete understanding of UML.   http://www.tutorialspoint.com/uml/index.html High Level Design (HLD) is the overall system design - covering the system architecture and database design. It describes the relation between various modules and functions of the system. data flow, flow charts and data structures are covered under HLD. Low Level Design (LLD) is like detailing the HLD. It defines the actual logic for each and every component of the system. Class diagrams with all the methods and relation between classes comes under LLD. Programs specs are covered under LLD. In HLD, you design the component level abstractions and interactions. In LLD, for each component, you go to the lower level such as class and method levels, describe what each class's responsibility, its interface and its interaction with other classes. All terms like "high...
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equals() and hashCode()

From the article Override equals and hashCode in Java: Default implementation of equals() class provided by java.lang.Object compares memory location and only return true if two reference variable are pointing to same memory location i.e. essentially they are same object. Java recommends to override equals and hashCode method if equality is going to be define by logical way or via some business logic: example: many classes in Java standard library does override it e.g. String overrides equals, whose implementation of equals() method return true if content of two String objects are exactly same Integer wrapper class overrides equals to perform numerical comparison etc.
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