sql to combine two unrelated tables into one - sql

Question

I have tables
table1
col1 col2
a b
c d
and table2
mycol1 mycol2
e f
g h
i j
k l
I want to combine the two tables, which have no common field into one table looking like:
table 3
col1 col2 mycol1 mycol2
a b e f
c d g h
null null i j
null null k l
ie, it is like putting the two tables side by side.
I'm stuck! Please help!

Answer 1

Get a row number for each row in each table, then do a full join using those row numbers:
WITH CTE1 AS
(
SELECT ROW_NUMBER() OVER(ORDER BY col1) AS ROWNUM, * FROM Table1
),
CTE2 AS
(
SELECT ROW_NUMBER() OVER (ORDER BY mycol1) AS ROWNUM, * FROM Table2
)
SELECT col1, col2, mycol1, mycol2
FROM CTE1 FULL JOIN CTE2 ON CTE1.ROWNUM = CTE2.ROWNUM
This is assuming SQL Server >= 2005.

Answer 2

It's really good if you put in a description of why this problem needs to be solved. I'm guessing it is just to practice sql syntax?
Anyway, since the rows don't have anything connecting them, we have to create a connection. I chose the ordering of their values. Also since they have nothing connecting them that also begs the question on why you would want to put them next to each other in the first place.
Here is the complete solution: http://sqlfiddle.com/#!6/67e4c/1
The select code looks like this:
WITH rankedt1 AS
(
SELECT col1
,col2
,row_number() OVER (order by col1,col2) AS rn1
FROM table1
)
,rankedt2 AS
(
SELECT mycol1
,mycol2
,row_number() OVER (order by mycol1,mycol2) AS rn2
FROM table2
)
SELECT
col1,col2,mycol1,mycol2
FROM rankedt1
FULL OUTER JOIN rankedt2
ON rn1=rn2

Answer 3

Option 1: Single Query
You have to join the two tables, and if you want each row in table1 to match to only one row in table2, you have to restrict the join somehow. Calculate row numbers in each table and join on that column. Row numbers are database-specific; here is a solution for mysql:
SELECT
t1.col1, t1.col2, t2.mycol1, t2.mycol2
FROM
(SELECT col1, col2, #t1_row := t1_row + 1 AS rownum FROM table1, (SELECT #t1_row := 0) AS r1) AS t1
LEFT JOIN
(SELECT mycol1, mycol2, #t2_row := t2_row + 1 AS rownum FROM table2, (SELECT #t2_row := 0) AS r2) AS t2
ON t1.rownum = t2.rownum;
This assumes table1 is longer than table2; if table2 is longer, either use RIGHT JOIN or switch the order of the t1 and t2 sub-selects. Also note that you can specify the order of each table separately using an ORDER BY clause in the sub-selects.
(See select increment counter in mysql)
Option 2: Post-processing
Consider making two selects, and then concatenating the results with your favorite scripting language. This is a much more reasonable approach.