The difference between union and join in sql

The difference between UNION and JOIN in SQL: UNION merges rows of tables with the same structure and eliminates duplicates; JOIN joins rows of tables based on conditions, allowing different structures. UNION performance is generally faster than JOIN, but requires the same structural table; JOIN is flexible but may have lower performance.

##The difference between UNION and JOIN in SQL

Get straight to the point:

UNION and JOIN are two commonly used operators in SQL for merging data from different tables. The main difference is how they combine rows in the table.

Detailed explanation:

UNION:

##UNION operation merges two or more tables with Rows with the same structure (i.e. same column names and data types).

• It creates a result set containing all unique rows, eliminating duplicates.
• Syntax:
SELECT ... UNION SELECT ...

JOIN:

##JOIN Operators join rows from one or more tables based on matching criteria.

It allows retrieving related data from multiple tables, even if the structure is different.
• Common JOIN types include: INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN.
• Syntax:
• SELECT ... FROM table1 JOIN table2 ON condition
• ##Comparison table:

FeaturesUNION##PurposeMerge with the same Rows of structure Join rows based on condition Result set Set of unique rows eliminating duplicates Based on match Set of conditional rowsColumn structureMust be the sameCan be differentMatching conditionsNoneSpecified in ON clausePerformanceUsually faster than JOINDepends on the table Size and connection complexityExample:

JOIN

UNION:

<code class="sql">SELECT * FROM table1
UNION
SELECT * FROM table2;</code>

JOIN:

<code class="sql">SELECT *
FROM table1
INNER JOIN table2 ON table1.id = table2.id;</code>

Note:

UNION can only join tables with the same structure. JOIN allows more flexibility in joining tables even if they have different structures.

For large data sets, the performance of JOIN may be lower than UNION.

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