Combining Two Queries in Oracle

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In this article, we will explore how to combine two queries in Oracle using various techniques. The example given in the question involves combining a query that contains negations and conditions with another query using the MINUS operator.

Background Information

The SQL language is used for managing data stored in relational database management systems such as Oracle. It provides several functionalities like data definition, data manipulation, and reporting.

Oracle uses various operators to perform operations on data, such as:

• IN: Used to test whether a value of a specified type or value matches a list of values.
• NOT IN: The opposite of the IN operator. It is used to select all records for which no row matches the criteria.
• MINUS (–): An operator that returns all rows from both queries that are not present in either.

Combining Queries

Using MINUS Operator

The original query using the MINUS operator can be seen as follows:

SELECT *
FROM table1 t1
WHERE t1.b_c IN ('A', 'B') AND t1.d_id IN ('2', '3')
AND (t1.a_d >= '2018-05-01' AND t1.a_d <= '2018-05-15')
AND (t1.a_m = 'AC' OR t1.a_m = 'NO')
AND t1.s = 'SW'
AND t1.c_m IN ('DM', 'SW')
AND t1.d_m IN ('DM', 'SW')
AND NOT ((t1.dept_id IN ('20', '35') AND
          (t1.a_m = 'AC' OR t1.a_m = 'NO')
          AND t1.s = 'SW'
          AND t1.c_m = 'DM'
          AND t1.d_m IN ('DM', 'SW')
          AND ((t1.o_b = 'X001' AND t1.s_s = 'X001') OR
               (t1.o_b = 'XXXX' AND t1.s_s = 'XXXX'))
          AND REGEXP_LIKE (t1.r_no, '^20PS|35RE$')));

To combine this query with another query using the MINUS operator, you can modify the original query to include only those conditions that are different from the first query.

Modified Query

SELECT *
FROM table1 t1
WHERE t1.b_c IN ('A', 'B') AND t1.d_id IN ('2', '3')
AND (t1.a_d >= '2018-05-01' AND t1.a_d <= '2018-05-15')
AND (t1.a_m = 'AC' OR t1.a_m = 'NO')
AND t1.s = 'SW'
AND t1.c_m IN ('DM', 'SW')
AND t1.d_m IN ('DM', 'SW')
AND NOT (
    (t1.dept_id IN ('20', '35') AND
     (t1.a_m = 'AC' OR t1.a_m = 'NO')
     AND t1.s = 'SW'
     AND t1.c_m = 'DM'
     AND t1.d_m IN ('DM', 'SW')
     AND ((t1.o_b = 'X001' AND t1.s_s = 'X001') OR
          (t1.o_b = 'XXXX' AND t1.s_s = 'XXXX'))
     AND REGEXP_LIKE (t1.r_no, '^20PS|35RE$')))

AND NOT (
    (t1.a_m, t1.s, t1.d_m, t1.c_m, t1.d_s) IN
    ((('NO', 'SW', 'SW', 'DM', 'X001'), ('NO', 'SW', 'SW', 'DM', 'XXXX')))

OR (t1.s, t1.d_m, t1.c_m) IN ((('SW', 'DM', 'SW')))
OR (t1.a_m, t1.s, t1.d_m, t1.c_m, t1.o_b, t1.b_b, t1.s_s) IN
    (((('AC', 'SW', 'DM', 'DM', 'XXXX'), ('AC', 'SW', 'DM', 'DM', 'X001'), 'XXXX'),
     ((('AC', 'SW', 'DM', 'DM', 'XXXX'), ('AC', 'SW', 'DM', 'DM', 'X001'), 'X001')),
     REGEXP_LIKE (t1.r_no, '^20PS|35RE$')));

Explanation

This modified query combines the two queries by including only those conditions that are different from the original set. The first part of the query checks for conditions that are present in both queries and excludes them using the NOT operator. The second part of the query checks for additional conditions that are present in the second query but not in the first one.

Conclusion

Combining two queries in Oracle can be achieved by including only those conditions that are different from the original set. This can be done using various techniques such as modifying the NOT IN operator or combining AND and OR operators to achieve the desired result.

Example Use Case

Suppose we have a table employees with the following structure:

We want to retrieve all employees who joined after May 15, 2018, and are not from the HR department.

SELECT *
FROM employees e1
WHERE e1.date_of_joining >= '2018-05-16'
AND e1.department != 'HR';

Using the modified query technique:

SELECT *
FROM employees e1
WHERE e1.date_of_joining >= '2018-05-01'
AND (e1.department = 'Marketing' OR e1.date_of_joining > '2018-06-01')
AND NOT (e1.department IN ('HR') AND
         (e1.name = 'John' OR e1.name = 'Jane'));

Both queries will return the same result:

Note that the modified query technique is more flexible and allows us to include additional conditions while excluding certain ones.

Last modified on 2024-03-25