How to find if a column is referenced in a computed column?
-
30-01-2021 - |
سؤال
I'm trying to mass retype columns. That means first dropping and recreating any constraints they are part of.
I found columns referenced by these constraints
- Foreign Keys,
- Primary Keys,
- Indexes,
- Check constraints,
- Rules,
- Default constraints.
But I cannot find Computed columns.
I've looked into INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE
, but it doesn't include Computed Columns.
There is also sys.computed_columns
which shows definition, but doesn't list columns in searchable manner.
Is there anywhere else I can look? If SQL Server can figure out the dependence, I thought I would be able to as well.
المحلول
Thanks to Scott Hodgin I found it in sys.sql_expression_dependencies
SELECT
OBJECT_NAME(sed.referencing_id) AS referencingTable
, pc.[name] AS computedColumn
, pc.is_computed
, cc.[name] AS referencedcolumn
, cc.is_computed
FROM sys.sql_expression_dependencies sed
JOIN sys.[columns] pc ON sed.referencing_minor_id = pc.column_id AND sed.referencing_id = pc.[object_id]
JOIN sys.[columns] cc ON sed.referenced_minor_id = cc.column_id AND sed.referenced_id = cc.[object_id]
WHERE sed.referencing_minor_id > 0 -- referencing object is Column
AND sed.referenced_minor_id > 0 -- referenced object is Column
AND sed.referencing_id = sed.referenced_id -- references the same table
نصائح أخرى
There is also sys.computed_columns which shows definition, but doesn't list columns in searchable manner.
If I understand correctly you want to find which columns are referenced by the computed column.
One solution would be searching the definition in sys.computed_columns
with CHARINDEX()
for each column where the object_id
matches
SELECT DISTINCT c.name,
cc.definition
FROM sys.columns c
CROSS APPLY
(
SELECT definition from sys.computed_columns cc
WHERE c.object_id = cc.object_id
AND CHARINDEX(c.name,cc.definition) > 0
) as cc;
Quick test
--Create a heap table.
CREATE TABLE dbo.test(id int,
val int);
-- add computed column on two columns.
ALTER TABLE dbo.test
ADD computedcolumn as id + val;
-- add a column that is not part of any computed column.
ALTER TABLE dbo.test
ADD bla int;
The query for one specific table
SELECT DISTINCT c.name,
cc.definition
FROM sys.columns c
CROSS APPLY
(
SELECT definition from sys.computed_columns cc
WHERE c.object_id = cc.object_id
AND CHARINDEX(c.name,cc.definition) > 0
) as cc
where c.object_id = object_id('dbo.test');
Result
name definition
id ([id]+[val])
val ([id]+[val])