07 DISTINCT in Oracle SQL TELUGU | PANDIT AJESH | SQL TUTORIALS #distinct #sqltelugu #plsql
Channel: PANDIT AJESH
Date: 2023-08-19

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1.  Understanding `DISTINCT` :
   The `DISTINCT` keyword is used to retrieve unique values from a column or a set of columns in a result set. It eliminates duplicate rows and only shows distinct values.

2.  Applying `DISTINCT` to Single Columns :
   You can use `DISTINCT` before a single column name to retrieve unique values from that column. For example:
   
    sql
   SELECT DISTINCT column_name FROM table_name;
    

3.  Using `DISTINCT` with Multiple Columns :
   You can apply `DISTINCT` to multiple columns to retrieve unique combinations of values across those columns. For example:

    sql
   SELECT DISTINCT column1, column2 FROM table_name;
    

4.  Order of Columns Matters :
   Keep in mind that when you use `DISTINCT` with multiple columns, it considers combinations of values across all selected columns. This means that `(A, B)` and `(B, A)` would be considered distinct if the order of columns matters in your data.

5.  Aggregates with `DISTINCT` :
   You can use aggregate functions like `COUNT`, `SUM`, `AVG`, etc., in combination with `DISTINCT` to perform calculations on unique values.

6.  Combining `DISTINCT` with Other Clauses :
   You can use the `DISTINCT` keyword in combination with other clauses like `WHERE`, `ORDER BY`, and `GROUP BY` to refine your result set.

7.  Performance Considerations :
   Using `DISTINCT` can have performance implications, especially on large datasets, as it involves sorting and eliminating duplicates. Be mindful of its impact and consider indexing columns if you frequently use `DISTINCT` on them.

8.  Using `GROUP BY` Instead :
   In some cases, using `GROUP BY` can be an alternative to achieve distinct values. This is particularly useful when you need to perform aggregate functions alongside distinct values.

9.  Filtering with `HAVING` :
   If you're using `GROUP BY` and want to filter aggregated results, you can use the `HAVING` clause instead of the `WHERE` clause, as `HAVING` works with aggregated values.

10.  Analytic Functions :
    Oracle SQL also offers analytic functions like `ROW_NUMBER()`, `RANK()`, and `DENSE_RANK()` which can help you identify distinct values based on specific conditions.



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