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SQL

  1. SQL Metadata

    by , 03-09-2012 at 08:30 PM
    Users and database information is stored itself in databases. Majority of DBMS consist of s set of system tables, which lists:
    • Tables in the database
    • Primary keys
    • Foreign keys
    • Column names in each table
    • Stored procedures



    Database features and table layout information is obtained by DBMS which consists of its own functions. Interface DatabaseMetaData is provided by the JDBC that shall be implemented by a driver writer. This is done information regarding DBMS ...
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  2. SQL Transactions

    by , 03-09-2012 at 08:29 PM
    In a database, at the same time two users might be accessing the similar data. E.g if one user is reading columnís value from database and other one is updating column at the same time. This is possible that 1st user may get old & update data, at the same time.
    To prevent these situations, transactions are provided by DBMS so that to maintain data in persistent state. More than 1 user may access database with data concurrency, at the same time.

    More than 1 SQL statements ...
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  3. Result Sets and Cursors

    by , 03-09-2012 at 08:28 PM
    Conditions of a query are satisfied by the result set. Result set is considered to be rows set. A result set can return no. of rows.
    • Zero
    • One
    • Many


    One user might obtain 1 row at one time. This functionality is supported by the cursor.
    Pointer and cursor are same which are present in a file that consists of many rows of the result set. Rows track is maintained by the pointer, which are accessible by the program. All rows top to bottom access is supported by a cursor, ...
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  4. SELECT Statements

    by , 03-09-2012 at 08:27 PM
    SQL is considered to be a query language which has been designed for using it with relational databases. Standard SQL commands set is present which is used along with all relational DMS i.e. database management system. All relational DBMS use select statement.

    Information is obtained from a table by select statement. This is also known as a query. Following is specified by it.
    • 1 or more columns
    • Selection criteria
    • 1 or more tables


    First & last names ...
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  5. Integrity Rules

    by , 03-09-2012 at 08:26 PM
    It shall be ensured by the relational tables that data is always accessible and accurate. To do this, implementation of the integrity rules is required. These rules shall be followed.
    • There shall be uniqueness in a tableís rows.
    • Correct results are not found easily and accessing data might result into certain issues. This happens when duplicate rows are present.


    Rules can be applied by user in most DBMS that duplicated rows are not permitted. In those cases, the insertion ...
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  6. What Can SQL do?

    by , 03-09-2012 at 08:25 PM
    • Against a database, queries can be executed by SQL.
    • From a database, data can be retrieved by SQL.
    • In a database, records can be inserted by SQL.
    • In a database, records can be updated by SQL.
    • From a database, records can be deleted by SQL.
    • New databases are created by SQL.
    • In a database, new tables are created by SQL.
    • In a database, stored procedures can be created by SQL.
    • In a database, views are created by SQL.
    • SQL can set permissions at procedures, views and tables.
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  7. Sql

    by , 03-09-2012 at 08:21 PM
    Databases are accessed by usage of a standard language SQL. It is used for the manipulation and also to access the data, in following.
    • MySQL
    • DB2
    • Access
    • Oracle
    • SQL Server
    • Sybase


    The SQL language consist of these language elements:

    • Clauses: Clauses are considered to be the constituent components of queries and statements.
    • Expressions: They can produce tabular data or scalar values which comprises of columns & rows.
    • Predicates: conditions
    ...
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