Rule: UNION Operators Should Be Surrounded by Newlines
Rule Code: LT11
Name: union_checks
Overview
In SQL queries, the UNION operator combines the result sets of two or more select statements. For clarity and readability, the UNION operator should be placed on its own line, surrounded by newlines before and after. This helps visually separate different parts of the query, making it easier to read and understand, especially when working with complex queries that involve multiple UNION operators.
Explanation
Anti-pattern: UNION Operator on the Same Line as Queries
Placing the UNION operator on the same line as one of the select statements can make the query harder to read and visually confusing. It may be difficult to distinguish between different parts of the query, especially in cases where multiple UNION operators are used.
Example of UNION Operator Without Newlines (Anti-pattern):
select foo.id, foo.name
from foo
union select bar.id,
bar.name
from bar;
In this example, the UNION operator is placed on the same line as the second select statement, which reduces readability and makes the query harder to follow.
Best Practice: UNION Operator Surrounded by Newlines
The UNION operator should be placed on a separate line, surrounded by newlines before and after. This visually separates each select statement, making the query more readable and easier to understand.
Refactored Example with UNION Operator on a Separate Line (Best Practice):
select foo.id,
foo.name
from foo
union
select bar.id,
bar.name
from bar;
In this refactored example, the UNION operator is placed on its own line, surrounded by newlines. This makes the query much clearer and easier to read, especially when working with more complex queries.
Conclusion
Placing UNION operators on their own line and surrounding them with newlines improves the readability and maintainability of SQL queries. By following this rule, developers ensure that their queries are easy to follow and less prone to errors.