Merge multiple tables into one table SQL Server

Question

I want to merge 3 tables into one only to get full data with conditions below

• merge 3 tables [test1], [test2], [test3] into one table [test]
• If when merging, if a column is blank select from another table
• Col1 exists in all 3 tables

Here is my example code to merge from table 2 into test.

MERGE INTO [dbo].[test] a
USING [dbo].[test2] b ON a.col1 = b.col1

WHEN MATCHED THEN
    UPDATE 
    SET col1 = b.col1,
        col2 = b.col2,
        col3 = b.col3,
        col4 = b.col4
    WHERE col1 = '' OR col2 = '' OR col3 = '' OR col4 = '';

It get errors:

Incorrect syntax near the keyword 'where'.

Answer 1

Please try the COALESCE function rather than using the where condition. The COALESCE function takes the next value in case there is a NULL is encountered.

    Merge into [dbo].[test] a   
    using [dbo].[test2] b
    on a.col1 = b.col1
    when matched then
    update
    set col2 = COALESCE(a.col2, b.col2),
    col3 = COALESCE(a.col3, b.col3),
    col4 = COALESCE(a.col4, b.col4);

So in the modified code, if the Table [dbo].[test] col2 is Null then it takes the value from [dbo].[test2]. Since you will be using COALESCE, you will be able to merge any number of values.

Answer 2

Can you show the table Structure.

you can use UNION ALL Operator follow this link.

https://www.techonthenet.com/sql_server/union.php

OR mixture of INNER JOIN with UPDATE statement combining the condition on WHERE clause