Question

I am having a Metadata table as below:

RULE_NAME      COL_NAME   COL_VAL
RULE_1     COL_1         ABC
RULE_1     COL_5         XYZ
RULE_2     COL_2         123
RULE_2     COL_3         A2d5
RULE_2     COL_8         X0IL
RULE_3     COL_1         PQR
RULE_3     COL_7         9789

I need to generate a WHERE clause using the data from this table. the WHERE clause should be like this:

WHERE
(COL_1 = 'ABC' AND COL_5 = 'XYZ') --from Rule 1 records
OR
(COL_2 = '123' AND COL_3 = 'A2D5' AND COL_8 = 'X0IL') --From Rule 2 records
OR
(COL_1 = 'PQR' AND COL_7 = '9789') --from Rule 3 records

Is this possible to do with normal SQL (I am on Teradata)? Can someone give me some pointers on how to achieve this?

Thanks.

Answer 1

The following returns each of the clauses on a separate line:

select oreplace(max(case when seqnum = 1 then clause else '' end) ||
                MAX(case when seqnum = 2 then clause else '' end) ||
                MAX(case when seqnum = 3 then clause else '' end)
               ), ')(', ') and (')
from (select t.*, ROW_NUMBER() over (partition by rule_name order by col_name) as seqnum,
             ('(' || COL_NAME || ' = ' || '''' || col_val || ''')') as clause
      from t
     ) t
group by rule_name

Is that close enough?

If you don’t have the ‘oreplace’ function, you can do something like:

select max(case when seqnum = 1 then clause else '' end) ||
       MAX(case when seqnum = 2 then clause else '' end) ||
       MAX(case when seqnum = 3 then clause else '' end) || ' 1=1 OR'
from (select t.*, ROW_NUMBER() over (partition by rule_name order by col_name) as seqnum,
             ('(' || COL_NAME || ' = ' || '''' || col_val || ''') and') as clause
      from t
     ) t
group by rule_name