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Database Articles
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Synonyms
When you reference an object in a SQL command that is owned by another user, you must preface the object name with the owner’s username. SELECT * FROM scott.dept ; A synonym is an alternate na…
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Indexes
A database index is a table that contains data values, along with a corresponding column that specifies the physical locations of the records (ROWID) that contain the associated sorted data values.…
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Database Views
A view does not physically exist in the database. It is derived from other database tables. When the data in its source table is updated , the view reflects the updates as well. If structure of a v…
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Selecting Records For Update
When you enter a SELECT command to query database records, no locks are placed on the selected records, and other database users can use view and update these records at the sane time you are viewin…
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Using Set Operators to Combine Query Results
Set Operator Purpose UNION Returns all rows from both queries, but displays duplicate rows only once. UNION ALL Returns all rows from both queriesi and displ…
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Creating Nested Query
A nested query is created when a second query, called a subquery, is nested within a main query. The main query is the first query that is listed in the SELECT command. The subquery is used to s…
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Joins - Joining Multiple Tables
The general syntax of a SELECT statement that joins two tables is : SELECT column1, column2, … FROM table1, table2 WHERE table1.join_column = table2.join_column ;
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Oracle SQL Group Functions
Function Description Example Result AVG (fieldname) Returns the average value of a numeric column’s returned values AVG (capacity ) 33.23030768…
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Oracle SQL Group Functions
Function Description Example Result AVG (fieldname) Returns the average value of a numeric column’s returned values AVG (capacity ) 33.23030768…
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Functions
SELECT inv_id, item_size, color, price,qoh, price * qoh FROM inventory WHERE item_id = 897; SELECT s_id, s_last, SYSDATE – s_dob FROM student ; SELECT s_id, s_last, ( SYSDATE – s_do…
Datawarehousing Articles
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Snowflake Schema
A snowflake schema is a term that describes a star schema structure normalized through the use of outrigger tables. i.e dimension table hierachies are broken into simpler tables.…
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Star Schema
When we consider an example of an organization selling products throughtout the world, the main four major dimensions are product, location, time and organization.…
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Data warehouse and Data Mart
Data Warehouse & Data MartA data warehouse is a relational/multidimensional database that is designed for query and analysis rather than transaction processing. A data warehouse usually contains histo…
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Datawarehouse defintion and Architecture
What is a Data Warehouse? According to Inmon, famous author for several data warehouse books, "A data warehouse is a subject oriented, integrated, time variant, non volatile collection of data in supp…
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Datawarehouse Vs Data Mart
Datawarehouse Data Mart Scope & Application Application Independent Specific Application A Data Warehouse is single point repository and its data can be used for any…
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Comparison of Data Warehouse and Operational Data
HOW IS THE WAREHOUSE DIFFERENT?The data warehouse is distinctly different from the operational data used and maintained by day-to-dayoperational systems. Data warehousing is not simply an “access wr…
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Data Warehouse Definitions
The data warehouse is that portion of an overall Architected Data Environment that serves as the singleintegrated source of data for processing information. The data warehouse has specific characteris…