Question

Table A

ID  COLA    
-----------------------
A   value1      
B   value1
C   value1      

Table B

ID  DETAIL_ID   COL_X   COL_Y
A   0           foo     foo
A   1           bar     bar
B   0           foo     foo

My expected out is something like

ID  COLA    COL_X_0 COL_X_1 COL_Y_0 COL_Y_1
A   value1  foo     bar     foo     bar
B   value1  foo     NULL    foo     NULL
C   value1  NULL    NULL    NULL    NULL

It means the rows of table B will be column values based on DETAIL_ID column.

I tried to write queries for this , but can’t succeed due to following.
Number of DetailID values will NOT be fixed-length.It means I can’t hard-coded the name of the columns.

Answer 1

SQL queries must specify the columns of the result set. That’s fundamental to SQL. Even PIVOT requires that your query specify the columns before you send it to the RDBMS.

For that reason, it’s difficult and error-prone to create a query that returns rows as columns as you describe, and can adapt as needed to any number of columns.

Handling dynamic columns must be a two-stage procedure.

One option is to make the two stages be:

1. Write application code to build the SQL query dynamically, based on the distinct values found in the data. This requires an extra query to discover what values exist so you can build the query.
2. Execute the SQL query and retrieve the results.

The other option is to make the two stages be:

1. Run a more plain SQL query, that fetches rows as rows, as they are stored in the database.
2. Write application code to post-process the results, collecting individual values from rows into an expanding set of columns based on the values found. This does not require an extra query as the first design does.