Category Archives: SQL

WALKUP TREES or Hierarchy AND INLINE VIEW

WALKUP TREES (Hierarchy) AND INLINE VIEW 

WALKUP TREES
Using hierarchical queries, you can retrieve data based on a natural hierarchical relationship between rows in a table. However, where a hierarchical relationship exists between the rows of a table, a process called tree walking enables the hierarchy to be constructed. Continue reading

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SUBQUERIES AND EXISTS

SUBQUERIES AND EXISTS

SUBQUERIES

  • Nesting of queries, one within the other is termed as a subquery.
  • A statement containing a subquery is called a parent query.
  • Subqueries are used to retrieve data from tables that depend on the values in the table itself. Continue reading

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JOINS

JOINS

The purpose of a join is to combine the data across tables.

  • A join is actually performed by the where clause which combines the specified rows of tables.
  • If a join involves in more than two tables then oracle joins first two tables based on the joins condition and then compares the result with the next table and so on. Continue reading

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