Finding a Primary Key Constraint on the fly in SQL

Question

I have the following SQL:

 ALTER TABLE dbo.PS_userVariables DROP CONSTRAINT PK_PS_userVariables;
 ALTER TABLE dbo.PS_userVariables ADD PRIMARY KEY (varnumber, subjectID, userID, datasetID, listid, userVarTitle);

Since I have multiple environments, that PK_PS_userVariables constraint name is different on my different databases. How do I write a script that gets that name then adds it into my script?

Answer 1

While the typical best practice is to always explicitly name your constraints, you can get them dynamically from the catalog views:

DECLARE @table NVARCHAR(512), @sql NVARCHAR(MAX);

SELECT @table = N'dbo.PS_userVariables';

SELECT @sql = 'ALTER TABLE ' + @table 
    + ' DROP CONSTRAINT ' + name + ';'
    FROM sys.key_constraints
    WHERE [type] = 'PK'
    AND [parent_object_id] = OBJECT_ID(@table);

EXEC sp_executeSQL @sql;

ALTER TABLE dbo.PS_userVariables ADD CONSTRAINT ...

Answer 2

DECLARE @TableName varchar(128)
DECLARE @IndexName varchar(128)
DECLARE @Command varchar(1000)

SET @TableName = 'PS_userVariables'

SELECT @IndexName = si.name
FROM sys.tables st
JOIN sys.indexes si ON st.object_id = si.object_id
WHERE st.name = @TableName
  AND si.is_primary_key = 1

SET @Command = 'ALTER TABLE dbo.' + QUOTENAME(@Tablename) + ' DROP CONSTRAINT ' + QUOTENAME(@IndexName) + ';
ALTER TABLE dbo.' + QUOTENAME(@Tablename) + ' ADD PRIMARY KEY (varnumber, subjectID, userID, datasetID, listid, userVarTitle);'

Answer 3

SELECT 
   A.TABLE_NAME, 
   A.CONSTRAINT_NAME, 
   B.COLUMN_NAME
FROM 
   INFORMATION_SCHEMA.TABLE_CONSTRAINTS A, 
   INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE B
WHERE 
      CONSTRAINT_TYPE = 'PRIMARY KEY' 
   AND A.CONSTRAINT_NAME = B.CONSTRAINT_NAME
ORDER BY 
   A.TABLE_NAME 

Ref: Pinal Dave @ http://blog.sqlauthority.com/2008/09/06/sql-server-find-primary-key-using-sql-server-management-studio/