SQL Server guessing missing foreign keys - sql-server

Question

I try to guess missing foreign keys using the following SQL code
DECLARE #ColumnList AS TABLE
(
TableName varchar(255) NOT NULL,
ColumnName varchar(255) NOT NULL,
PKTableName varchar(255),
PKColumnName varchar(255),
HasForeignKey bit NOT NULL
)
-- Find all column names that occur more than once.
-- Exclude archive and staging tables.
INSERT INTO #ColumnList
(TableName,
ColumnName,
PKTableName,
PKColumnName,
HasForeignKey)
SELECT t.NAME AS TableName,
c.NAME AS ColumnName,
NULL AS PKTableName,
NULL AS PKColumnName,
CASE
WHEN f1.parent_object_id IS NOT NULL THEN 1
WHEN f2.referenced_object_id IS NOT NULL THEN 1
ELSE 0
END AS HasForeignKey
FROM sys.tables AS t
JOIN sys.columns AS c
ON c.object_id = t.object_id
JOIN sys.types AS y
ON c.system_type_id = y.system_type_id
LEFT JOIN sys.foreign_key_columns AS f1
ON f1.parent_object_id = t.object_id AND f1.parent_column_id = c.column_id
LEFT JOIN sys.foreign_key_columns AS f2
ON f2.referenced_object_id = t.object_id AND f2.referenced_column_id = c.column_id
WHERE t.is_ms_shipped = 0 AND y.NAME IN ('bigint', 'int', 'smallint', 'tinyint', 'uniqueidentifier');
SELECT TableName,
ColumnName,
PKTableName,
PKColumnName
FROM #ColumnList
WHERE HasForeignKey = 0
AND ColumnName IN (SELECT ColumnName
FROM #ColumnList
GROUP BY ColumnName
HAVING Count(*) > 1)
ORDER BY ColumnName,
TableName;
That works fine and displays many candidates. I do not know, however, how to display the table name and the column name of the possible primary key. Any help will be appreciated.

Answer 1

Try this
DECLARE #ColumnList AS TABLE
(
TableName varchar(255) NOT NULL,
ColumnName varchar(255) NOT NULL,
PKTableName varchar(255),
PKColumnName varchar(255),
HasForeignKey bit NOT NULL
)
-- Find all column names that occur more than once.
-- Exclude archive and staging tables.
INSERT INTO #ColumnList
(TableName,
ColumnName,
PKTableName,
PKColumnName,
HasForeignKey)
SELECT t.NAME AS TableName,
c.NAME AS ColumnName,
t2.NAME AS PKTableName,
c2.NAME AS PKColumnName,
CASE
WHEN f1.parent_object_id IS NOT NULL THEN 1
WHEN f2.referenced_object_id IS NOT NULL THEN 1
ELSE 0
END AS HasForeignKey
FROM sys.tables AS t
JOIN sys.columns AS c
ON c.object_id = t.object_id
JOIN sys.types AS y
ON c.system_type_id = y.system_type_id
LEFT JOIN sys.columns c2
ON (c.Name = c2.Name)
JOIN sys.tables t2
ON (c2.object_id = t2.object_id AND t.object_id <> t2.object_id)
LEFT JOIN sys.foreign_key_columns AS f1
ON f1.parent_object_id = t.object_id AND f1.parent_column_id = c.column_id
LEFT JOIN sys.foreign_key_columns AS f2
ON f2.referenced_object_id = t.object_id AND f2.referenced_column_id = c.column_id
WHERE t.is_ms_shipped = 0 AND y.NAME IN ('bigint', 'int', 'smallint', 'tinyint', 'uniqueidentifier');
SELECT TableName,
ColumnName,
PKTableName,
PKColumnName
FROM #ColumnList
WHERE HasForeignKey = 0
AND ColumnName IN (SELECT ColumnName
FROM #ColumnList
GROUP BY ColumnName
HAVING Count(*) > 1)
ORDER BY ColumnName,
TableName;

Answer 2

I would try doing a LEFT OUTER JOIN to primary keys based on the column name:
LEFT OUTER JOIN
(
INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC
INNER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE CCU ON
CCU.CONSTRAINT_CATALOG = TC.CONSTRAINT_CATALOG AND
CCU.CONSTRAINT_SCHEMA = TC.CONSTRAINT_SCHEMA AND
CCU.CONSTRAINT_NAME = TC.CONSTRAINT_NAME AND
CCU.TABLE_CATALOG = TC.TABLE_CATALOG AND
CCU.TABLE_SCHEMA = TC.TABLE_SCHEMA AND
CCU.TABLE_NAME = TC.TABLE_NAME
) ON
CCU.COLUMN_NAME = C.ColumnName AND -- Use the #ColumnList.ColumnName here
TC.CONSTRAINT_TYPE = 'PRIMARY KEY'
This breaks down a bit with composite PKs. It also won't work if the names don't match - for example, some people will use "id" for the PK of "Person", but in the FK it would be "person_id".