Question

When writing views and nesting views within deeper views I sometimes miss something and end up losing rows/data. How can I check that columns from two different tables have an exact match of data?

Example:

select count(distinct table1.col1)
  from table1
 where table1.col1 not in (select distinct table2.col1 
                             from table2);

This would return the number of values in table1.col1 that are not in table2. However, I don’t know that this is a good solution as it doesn’t count the table2.col1 values that do not exist in table1.col1.

Answer 1

Use:

SELECT MAX(x.t1_missing_count) AS t1_missing_count, 
       MAX(x.t2_missing_count) AS t2_missing_count
  FROM (
SELECT COUNT(DISTINCT t1.col1) AS t1_missing_count,
       NULL AS t2_missing_count
  FROM TABLE_1 t1
 WHERE t1.col1 NOT IN (SELECT DISTINCT t2.col1 
                         FROM TABLE_2 t2)
UNION ALL
SELECT NULL,
       COUNT(DISTINCT t2.col1),           
  FROM TABLE_2 t2
 WHERE t2.col1 NOT IN (SELECT DISTINCT t1.col1 
                         FROM TABLE_1 t1)) x