Update table with matching primary keys - sql

Question

I have two tables TABLE1 and TABLE2.
I need to update TABLE1 with the matching primary keys from TABLE2.
Here is my code to get the primary key from TABLE1:
SELECT C.COLUMN_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS T
JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE C ON C.CONSTRAINT_NAME = T.CONSTRAINT_NAME
WHERE C.TABLE_NAME = 'TABLE1'
AND T.CONSTRAINT_TYPE = 'PRIMARY KEY'
This is the code to get primary key for TABLE2:
SELECT C.COLUMN_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS T
JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE C ON C.CONSTRAINT_NAME = T.CONSTRAINT_NAME
WHERE C.TABLE_NAME = 'TABLE2'
AND T.CONSTRAINT_TYPE = 'PRIMARY KEY'
And this code is used to update TABLE1:
MERGE INTO <TABLE1>
USING <TABLE2> ON (TABLE1.COLUMN_NAME = TABLE2.COLUMN_NAME)
WHEN MATCHED THEN
UPDATE
SET <TABLE1.COLUMN_NAME> = <TABLE1.COLUMN_NAME>
I need to merge all snippets of code to update the TABLE1, please help me how to get the primary keys and update with a single code.

Answer 1

As #GuidoG recommended, you will probably need to use dynamic SQL to perform this feat. Furthermore, from your question it is hard to figure out how to determine that Table1 and Table2 are related to one another.
Let us suppose that you have a table with table pairs available, and Table1 and Table 2 are one of those pairs. We'll need to figure out what the primary keys of both tables are, and then build the dynamic SQL using this information.
DECLARE #tableCombinations TABLE ([MainTable] NVARCHAR(255), [SubTable] NVARCHAR(255))
INSERT INTO #tableCombinations ([MainTable], [SubTable]) VALUES ('Table1','Table2')
DECLARE #q NVARCHAR(MAX) = ''
;WITH PrimaryKeys AS (
SELECT [Schema_Name] = sch.[name]
, [Table_Name] = tbl.[name]
, [Column_Name] = cols.[name]
FROM [sys].[indexes] i
JOIN [sys].[index_columns] ic ON i.[index_id] = ic.[index_id] AND i.[object_id] = ic.[object_id]
JOIN [sys].[columns] cols ON cols.[object_id] = ic.[object_id] AND cols.[column_id] = ic.[column_id]
JOIN [sys].[tables] tbl ON ic.[object_id] = tbl.[object_id]
JOIN [sys].[schemas] sch ON tbl.[schema_Id] = sch.[schema_id]
WHERE i.[is_primary_key] = 1
)
SELECT #q += 'MERGE INTO ' + QUOTENAME(pkMain.[Schema_Name]) + '.' + QUOTENAME(pkMain.[Table_Name]) +' mt
USING ' + QUOTENAME(pkSub.[Schema_Name]) + '.' + QUOTENAME(pkSub.[Table_Name]) + 'st ON (
mt.' + QUOTENAME(pkMain.[Column_Name]) + ' = st.' + pkSub.[Column_Name] + ')
WHEN MATCHED THEN UPDATE SET mt.' + QUOTENAME(pkMain.[Column_Name]) + ' = st.' + pkSub.[Column_Name] + ';' + CHAR(13) + CHAR(10)
FROM #tableCombinations tc
JOIN [PrimaryKeys] pkMain ON tc.[MainTable] = pkMain.[Table_Name]
JOIN [PrimaryKeys] pkSub ON tc.[SubTable] = pkSub.[Table_Name]
SET #q = REPLACE(#q, ' ', '')
SELECT #q
Of course, if this yields the correct results, you can directly execute this query using [sys].[sp_executesql]. For more reliable results, be sure to include the schema names of the table combinations.