[Solved] You have two queries:1) SELECT id, name FROM Employees WHERE department = 'HR'2) SELECT id, name FROM Contractors WHERE department = 'HR'You want to combine these queries to get all rows including... | PostgreSQL

PostgreSQL - Set Operations and Advanced Queries

You have two queries:
1) SELECT id, name FROM Employees WHERE department = 'HR'
2) SELECT id, name FROM Contractors WHERE department = 'HR'

You want to combine these queries to get all rows including duplicates. Which query achieves this?

ASELECT id, name FROM Employees WHERE department = 'HR' UNION SELECT id, name FROM Contractors WHERE department = 'HR';

BSELECT id, name FROM Employees WHERE department = 'HR' UNION ALL SELECT id, name FROM Contractors WHERE department = 'HR';

CSELECT id, name FROM Employees WHERE department = 'HR' INTERSECT SELECT id, name FROM Contractors WHERE department = 'HR';

DSELECT id, name FROM Employees WHERE department = 'HR' EXCEPT SELECT id, name FROM Contractors WHERE department = 'HR';

Step-by-Step Solution

Solution:

Step 1: Understand requirement
We want all rows from both queries including duplicates.
Step 2: Choose correct operator
UNION ALL combines results and keeps duplicates; UNION removes duplicates.
Step 3: Analyze options
SELECT id, name FROM Employees WHERE department = 'HR' UNION ALL SELECT id, name FROM Contractors WHERE department = 'HR'; uses UNION ALL, which fits the requirement.
Final Answer:
SELECT id, name FROM Employees WHERE department = 'HR' UNION ALL SELECT id, name FROM Contractors WHERE department = 'HR'; -> Option B
Quick Check:
Use UNION ALL to keep duplicates [OK]

Quick Trick: UNION ALL keeps duplicates, UNION removes them [OK]

Common Mistakes:

Using UNION instead of UNION ALL
Confusing INTERSECT or EXCEPT with UNION
Not matching column names and types

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You have two queries:

Step 1: Understand requirement

Step 2: Choose correct operator

Step 3: Analyze options

Final Answer:

Quick Check:

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