SQL UNION – Stack Corresponding Columns Vertically

At the core of any business are its data. Effectively analyzing and interpreting this data can lead to valuable insights that can guide decision-making and drive success. Here’s where SQL (Structured Query Language) comes into play — it’s the language of databases, enabling us to query, manipulate, and retrieve data with precision. One of the essential commands in SQL is UNION, a versatile tool for combining data from multiple tables or queries into a single cohesive result set. In this blog, we’ll delve deeper into UNION and explore how it can be used to stack corresponding columns vertically.

UNION Unveiled: Joining Forces to Combine Data

Imagine you’re working on a business analysis project where you need to consolidate data from various sources, such as customer information, sales records, and product details. Instead of manually merging these disparate datasets, UNION provides a swift and efficient solution. It serves as a data unifier, merging rows from multiple tables or queries based on specific criteria.

sql
SELECT * FROM Table1
UNION
SELECT * FROM Table2;

Syntax Breakdown:

• SELECT *: Retrieves all columns and rows from both tables.
• FROM Table1 and FROM Table2: Specifies the tables to be combined.
• UNION: The command that merges the results from both queries.

Vertically Stacking Columns: A Structured Approach

While UNION merges rows horizontally, it also has a hidden superpower — the ability to stack columns vertically. This technique is particularly useful when you want to compare data from different tables or queries that share common columns. Here’s how it’s done:

sql
SELECT column1, column2, column3
FROM Table1
UNION
SELECT column1, column2, column3
FROM Table2;

Outcome:

| column1 | column2 | column3 |
|—|—|—|
| Value 1.1 | Value 1.2 | Value 1.3 |
| Value 2.1 | Value 2.2 | Value 2.3 |

Advantages Galore: Unveiling the Benefits of UNION

UNION, with its ability to vertically stack columns, offers a plethora of benefits for business analysts:

• Data Consolidation: Effortlessly merge data from various sources into a single comprehensive dataset, simplifying analysis and decision-making.
• Enhanced Data Comparison: Facilitate side-by-side comparisons of data from different tables or queries, uncovering patterns and trends that might be hidden when viewed separately.
• Versatile Query Construction: Combine queries seamlessly to extract specific data elements or perform complex analysis, unlocking insights that drive business growth.

When UNION Falls Short: Understanding Its Limitations

While UNION is a powerful tool, it does have a few limitations:

• Similar Column Structures: UNION can only merge tables or queries with identical column structures. If the columns don’t match, you’ll face error messages and incomplete results.
• Data Type Consistency: Columns being merged must have compatible data types. Mixing different data types can lead to errors or data corruption.
• Distinct Values Only: UNION eliminates duplicate rows by default. If you need to retain duplicates, consider using the UNION ALL variation.

Frequently Asked Questions: Demystifying UNION

Q1: What’s the difference between UNION and UNION ALL?

A: UNION removes duplicate rows from the combined result set, while UNION ALL retains all rows, including duplicates.

Q2: Can I use UNION to combine data from different databases?

A: Yes, but ensure that the databases are compatible and the tables have identical column structures.

Q3: How can I handle columns with different names when using UNION?

A: Use column aliases to assign temporary names to columns, enabling them to be merged even if their original names differ.

Conclusion: Unifying Data, Empowering Analysis

SQL UNION, with its ability to stack corresponding columns vertically, is an invaluable tool for business analysts seeking to consolidate and compare data from multiple sources. By leveraging UNION’s capabilities, analysts can uncover valuable insights, identify trends, and make informed decisions that drive business success. Embrace the power of UNION and unlock the full potential of your data!