Query to find field duplicate between 9 tables - sql

Question

I have 9 tables each with value like
Level_1_tab
Code Name
ae1 hdgdgd
ae2 dhdh
level_2_tab
code Name
2 jfjfjf
3 fkfjfjf
similarly level_3_tab , level_4_tab, level_5 table so on and so forth till level_9_tab.
I am inserting the code column into a new table and checking for duplicates.
SELECT
code, name, COUNT(*)
FROM
new_table
GROUP BY
code, name
HAVING
COUNT(*) > 1;
Can i write a query and compare the code column of these 9 tables and check for duplicates ? that all the rows with duplicate code values should be retrieved

Answer 1

You can do a union all of the 9 tables and run your same query on that.
select code, name, count(*) from
(select code, name from table 1 union all
select code, name from table 2 union all
select code, name from table 3 union all
select code, name from table 4 union all
.....)
group by code, name
having count(*) > 1;

Answer 2

Everyone's suggestion of union all is great to build your initial table to look for duplicates in. But you say you already have a temp table with all of the values from the 9 tables which is perfect and another great way of doing it if your dataset isn't huge.
The only step your missing from your description to get the actually duplicate rows is to use your duplicate query above to re-query your temp table and return the rows you want. A great way of doing this is through common table expressions which basically allows you to build a query on top of your other query without another temp table. So use a cte and join back to your temp table.
;WITH CommonTableExpression AS (
SELECT
code, name, COUNT(*)
FROM
new_table
GROUP BY
code, name
HAVING
COUNT(*) > 1;
)
SELECT t.*
FROM
new_table t
INNER JOIN CommonTableExpression c
ON t.code = c.code
AND t.name = c.name
If you want to do it to each of the 9 tables independently rather than to your temp table. Place the duplicates into another temp table and join on it.
SELECT
code, name, COUNT(*)
INTO #Duplicates
FROM
new_table
GROUP BY
code, name
HAVING
COUNT(*) > 1
SELECT
l.*
FROM
leve_1_tab l
INNER JOIN #Duplicates d
ON l.Code = d.Code
AND l.name = d.name
Seeing everyone loves union all here is a way to do it with out temp tables and lots of union all s I wonder which would be a more optimized query though.
;WITH cteAllCodeValues AS (
select code, name from table 1 union all
select code, name from table 2 union all
select code, name from table 3 union all
select code, name from table 4 union all
--.....)
)
, cteDuplicates AS (
SELECT code, name, RecordCount = COUNT(*)
FROM
cteAllCodeValues
GROUP BY
code, name
)
SELECT c.*
FROM
cteDuplicates d
INNER JOIN cteAllCodeValues c
ON d.code = c.code
AND d.name = c.name