ORACLE Connect by clause equivalent in SQL Server
Is there a equivalent clause to CONNECT BY of Oracle in SQL Server. The requirement to build a category tree using a parentId f开发者_JS百科ield.
The SQL Server 2005+ equivalent of Oracle's CONNECT BY
hierarchical query syntax is to use a recursive CTE. SQL Server 2008 added HierarchyID. Here's an example of a recursive CTE:
WITH EmployeeHierarchy (EmployeeID, LastName, FirstName, ReportsTo, HierarchyLevel) AS (
SELECT EmployeeID,
LastName,
FirstName,
ReportsTo,
1 as HierarchyLevel
FROM Employees
WHERE ReportsTo IS NULL
UNION ALL
-- Recursive step
SELECT e.EmployeeID,
e.LastName,
e.FirstName,
e.ReportsTo,
eh.HierarchyLevel + 1 AS HierarchyLevel
FROM Employees e
JOIN EmployeeHierarchy eh ON e.ReportsTo = eh.EmployeeID)
SELECT *
FROM EmployeeHierarchy
ORDER BY HierarchyLevel, LastName, FirstName
Googling "hierarchical CTE" and/or "recursive CTE" will turn up numerous results. I took the example query from the 4GuysFromRolla.com.
Recursive CTEs are now ANSI standard - the syntax wasn't supported until Oracle 11g as I understand.
There's HierarchyID data type in MS SQL Server 2008, which can make your life easier.
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