How do I get constraints on a SQL Server table column - sql

Question

I have a column called MealType (VARCHAR) in my table with a CHECK constraint for {"Veg", "NonVeg", "Vegan"}
That'll take care of insertion.
I'd like to display these options for selection, but I couldn't figure out the SQL query to find out the constraints of a particular column in a table.
From a first glance at system tables in SQL Server, it seems like I'll need to use SQL Server's API to get the info. I was hoping for a SQL query itself to get it.

Answer 1

Easiest and quickest way is to use:
sp_help 'TableName'

Answer 2

This query should show you all the constraints on a table:
select chk.definition
from sys.check_constraints chk
inner join sys.columns col
on chk.parent_object_id = col.object_id
inner join sys.tables st
on chk.parent_object_id = st.object_id
where
st.name = 'Tablename'
and col.column_id = chk.parent_column_id
can replace the select statement with this:
select substring(chk.Definition,2,3),substring(chk.Definition,9,6),substring(chk.Definition,20,5)

Answer 3

SELECT obj_table.NAME AS 'table',
columns.NAME AS 'column',
obj_Constraint.NAME AS 'constraint',
obj_Constraint.type AS 'type'
FROM sys.objects obj_table
JOIN sys.objects obj_Constraint
ON obj_table.object_id = obj_Constraint.parent_object_id
JOIN sys.sysconstraints constraints
ON constraints.constid = obj_Constraint.object_id
JOIN sys.columns columns
ON columns.object_id = obj_table.object_id
AND columns.column_id = constraints.colid
WHERE obj_table.NAME='table_name'
ORDER BY 'table'

Answer 4

You can use
sp_helpconstraint 'tableName', 'nomsg'
to get all the constraints for the table.
"sp_help" return far more information.

Answer 5

Thanks to orgtrigger for his example!
I improved it to be able to remove unnecessary constraints (and then create their modified versions, if needed). Maybe this code will be useful for anybody.
-- removing old constraints
DECLARE #ConstraintNames TABLE (Name VARCHAR(MAX), RowNum INT)
DECLARE #TableName VARCHAR(100) = 'HubSpot'
INSERT #ConstraintNames
SELECT [constraint].name,
ROW_NUMBER() OVER (ORDER BY [constraint].[name]) AS RowNum
FROM sys.default_constraints [constraint]
INNER JOIN sys.columns col
ON [constraint].parent_object_id = col.object_id
INNER JOIN sys.tables st
ON [constraint].parent_object_id = st.object_id
WHERE
st.name = #TableName
AND col.name IN ('ForceUpdateOnImport', 'ForceUpdateOnExport')
AND col.column_id = [constraint].parent_column_id
SELECT * FROM #ConstraintNames
DECLARE #i INT = 1,
#count INT,
#constraintName VARCHAR(MAX),
#sql VARCHAR(MAX)
SELECT #count = COUNT(1) FROM #ConstraintNames
WHILE #i <= #count
BEGIN
SELECT #constraintName = cn.Name FROM #ConstraintNames cn WHERE cn.RowNum = #i
SET #sql = 'ALTER TABLE ' + #TableName + ' DROP CONSTRAINT ' + #constraintName
EXEC (#sql)
SET #i = #i + 1
END

Answer 6

Below is helpful for check and default constraints. I use it for implicit constraints to offer up guidance for what the name should be. If you remove everything after the where clause, it should be good for any check/default constraints.
SELECT /* obj_table.NAME AS 'table',
columns.NAME AS 'column',
obj_Constraint.NAME AS 'constraint',
obj_Constraint.type AS 'type',
sss.name as 'schema',*/
'ALTER TABLE [' + ltrim(rtrim(sss.name))+'].['+ltrim(rtrim(obj_table.name)) + '] DROP CONSTRAINT [' + obj_Constraint.NAME + '];' As 'Wrong_Implicit_Constraint',
'ALTER TABLE [' + ltrim(rtrim(sss.name))+'].['+ltrim(rtrim(obj_table.name)) + '] ADD CONSTRAINT [' + CASE obj_Constraint.type
WHEN 'D' THEN 'DF' WHEN 'F' THEN 'FK'
WHEN 'U' THEN 'UX' WHEN 'PK' THEN 'PK' WHEN 'N' THEN 'NN' WHEN 'C' THEN 'CK'
END + '_' + ltrim(rtrim(obj_table.name)) + '_' + columns.NAME + ']' +
CASE obj_Constraint.type WHEN 'D' THEN ' DEFAULT (' + dc.definition +') FOR [' + columns.NAME + ']'
WHEN 'C' THEN ' CHECK (' + cc.definition +')'
ELSE '' END +
';' As 'Right_Explicit_Constraint'
FROM sys.objects obj_table
JOIN sys.objects obj_Constraint ON obj_table.object_id = obj_Constraint.parent_object_id
JOIN sys.sysconstraints constraints ON constraints.constid = obj_Constraint.object_id
JOIN sys.columns columns ON columns.object_id = obj_table.object_id
AND columns.column_id = constraints.colid
left join sys.schemas sss on obj_Constraint.schema_id=sss.schema_id
left join sys.default_constraints dc on dc.object_id = obj_Constraint.object_id
left join sys.check_constraints cc on cc.object_id = obj_Constraint.object_id
WHERE obj_Constraint.type_desc LIKE '%CONSTRAINT'
AND RIGHT(obj_Constraint.name,10) LIKE '[_][_]________' --match double underscore + 8 chars of anything
AND RIGHT(obj_Constraint.name,8) LIKE '%[A-Z]%' --Ensure alpha in last 8
AND RIGHT(obj_Constraint.name,8) LIKE '%[0-9]%' --Ensure numeric in last 8
AND RIGHT(obj_Constraint.name,8) not LIKE '%[^0-9A-Z]%' --Ensure no special chars