Merge and append queries are two fundamental data transformation operations in Power Query Editor that allow you to combine data from multiple sources in Power BI.
**Append Queries**
Append queries stack tables vertically, combining rows from two or more tables into a single table. This operation…Merge and append queries are two fundamental data transformation operations in Power Query Editor that allow you to combine data from multiple sources in Power BI.
**Append Queries**
Append queries stack tables vertically, combining rows from two or more tables into a single table. This operation is similar to a SQL UNION. When you append queries, Power BI adds all rows from the second table below the rows of the first table. This is particularly useful when you have data split across multiple files or tables with identical structures, such as monthly sales reports or regional data files. The columns should have matching names and data types for optimal results. You can append two tables or append multiple tables at once using the 'Append Queries as New' option to create a new combined table while preserving the original sources.
**Merge Queries**
Merge queries combine tables horizontally by joining them based on matching values in one or more columns, similar to SQL JOIN operations. Power BI supports several join types: Left Outer (all rows from left table), Right Outer (all rows from right table), Full Outer (all rows from both tables), Inner (only matching rows), Left Anti (rows in left not in right), and Right Anti (rows in right not in left). When merging, you select the matching columns from each table to establish the relationship. The result includes columns from both tables, with the second table's data appearing as a nested table that you can expand to show individual columns.
**Key Differences**
- Append increases row count by stacking data vertically
- Merge increases column count by joining data horizontally
- Append requires similar table structures
- Merge requires common key columns for matching
Both operations are performed in Power Query Editor and are essential for consolidating disparate data sources into cohesive datasets for analysis and reporting in Power BI.
Merge and Append Queries in Power BI
Why Merge and Append Queries Matter
Understanding merge and append operations is essential for the PL-300 exam because data rarely comes from a single source. In real-world scenarios, you'll need to combine data from multiple tables to create meaningful reports. These operations are fundamental to data preparation and transformation in Power Query Editor.
What Are Merge and Append Queries?
Append Queries: This operation stacks tables vertically, adding rows from one or more tables to another. Think of it as combining tables that have the same structure but different records. For example, appending sales data from January, February, and March into a single table.
Merge Queries: This operation joins tables horizontally based on matching columns, similar to SQL joins. You use merge when you need to bring columns from one table into another based on a common key. For example, merging a Sales table with a Products table to add product details to each sale.
How Merge Queries Work
Power BI offers six types of joins when merging:
• Left Outer - All rows from the first table, matching rows from the second • Right Outer - All rows from the second table, matching rows from the first • Full Outer - All rows from both tables • Inner - Only rows that match in both tables • Left Anti - Rows from the first table that have no match in the second • Right Anti - Rows from the second table that have no match in the first
To perform a merge: Open Power Query Editor → Select Home tab → Click Merge Queries → Choose the tables and matching columns → Select join type → Expand the merged column to select desired fields.
How Append Queries Work
Append operations combine tables with similar structures:
• Two Tables - Append one table to another • Three or More Tables - Use 'Append Queries as New' to combine multiple tables
To perform an append: Open Power Query Editor → Select Home tab → Click Append Queries → Choose tables to append → Click OK. Columns with matching names align; mismatched columns result in null values.
Key Differences to Remember
• Append = Vertical combination (adds rows) • Merge = Horizontal combination (adds columns) • Append requires similar column structures • Merge requires a common key column
Exam Tips: Answering Questions on Merge and Append Queries
1. Identify the scenario type: If the question mentions combining same-structured tables or adding rows, think Append. If it mentions joining tables on a key or adding columns, think Merge.
2. Know your join types: The exam frequently tests understanding of Left Outer vs Inner vs Left Anti joins. Remember that Left Outer keeps all records from the primary table, Inner keeps only matches, and Left Anti keeps only non-matches.
3. Watch for keywords: 'Combine monthly files' suggests Append. 'Add customer names to orders' suggests Merge.
4. Remember the location: Both operations are found in Power Query Editor under the Home tab, not in the main Power BI Desktop interface.
5. Understand Merge Queries vs Merge Queries as New: 'Merge Queries' modifies the current query, while 'Merge Queries as New' creates a separate query.
6. Consider null values: Questions may test your knowledge of what happens when matches aren't found—this depends on the join type selected.
7. Native query folding: Be aware that some merge operations may prevent query folding, which impacts performance on large datasets.
8. Fuzzy matching: Know that Power BI supports fuzzy matching for merges when exact matches aren't possible, useful for handling slight variations in text data.