Recursive Queries in sql
In SQL database management systems, a recursive query is a database query custom-generated by the database user that automatically calls itself when a particular portion of the table query is run multiple times until a base table query condition or logic expression applied by the database user is met. Recursive queries developed in database tables are very useful for previewing hierarchical or tree-like data formats in a specific order, such as organizational data structure formats, file system data, or bill-of-material (BOM) hierarchies.
Recursive queries in SQL database tables are typically created using common table expressions (CTEs) using the WITH RECURSIVE clause command or statement. Here, the database user can analyse the query by dividing it into two parts.
Elements of a recursive query.
- Anchor member – This is the base case in a recursive query, which creates the starting set of table rows as output.
- Recursive member – This is the portion in a recursive query that indicates or relates to the CTE itself, and automatically calls itself until the recursive query condition is met in the database table.
Syntax of a recursive CTE in an SQL database table.
WITH RECURSIVE cte_emp_name AS (
//Anchor member: This is the base case of the recursion query
SELECT column1, column2, …
FROM table_name
WHERE some_condition
UNION ALL
//Recursive member: This is the part of the query that indicates the references with the CTE features
SELECT column1, column2, …
FROM table_name
INNER JOIN cte_emp_name ON table_emp_name.column = cte_emp_name.column
WHERE some_condition
)
SELECT * FROM cte_emp_name;
Element of a recursive query in SQL.
- WITH RECURSIVE – This is a reserved keyword that tells the SQL database to create a recursive CTE query.
- Anchor member – This indicates the first SELECT command or statement in a recursive query, starting the result output set.
- UNION ALL – This grouping is used to group the anchor member and the recursive member in a recursive query. The UNION ALL statement in a recursive query is typically used to avoid duplicate deletions. However, if the database user requires a different output result, they can apply the UNION keyword.
- Recursive Member – This is the second SELECT command or statement in a recursive query that automatically references its own CTE when the recursive query is run, and returns after calling the recursion.
- Termination Condition – This is where the recursion task continues in the database table until the recursive member returns a new row value.
Recursive Queries in SQL Conclusion.
Recursive queries are a popular and essential tool in SQL database management systems for applying recursive query tasks to hierarchical or tree-structured data. These help database users analyse tabular data relationships such as organizational hierarchical table data, file system concepts, or BOM (Bill-of-Materials) structures. By applying recursive CTE features with the WITH RECURSIVE clause statement, database users can break down and divide complex hierarchical tabular data into manageable, structured results. Here, while dealing with recursive queries, database users must have a correct recursive query base case and termination program condition logic or expression to stop or control an infinite recursion and performance expression logic error.
