如何在 Oracle 查询中使用查找

Question

I have a reference table called customer that has cust_id, cust_name ..., there are also other tables that have cust_name, cust_location....so on. I need to look up cust_location using cust_name from all these tables. how do I write the query in oracle SQL?

select cust_id, cust_name from customer
from (
    select cust_name as cust_location from tb1
    union all
    select cust_name as cust_location from tbl2
    union all
    select cust_name as cust_location from tbl3
    )

expected result.......looks like

Answer 1

You were nearly there..

select cust_location, table_name
from (
    select cust_name as cust_location, 'tb1' as table_name from tb1
    union all
    select cust_name as cust_location, 'tb2' as table_name from tbl2
    union all
    select cust_name as cust_location, 'tb3' as table_name from tbl3
    )

You can get Oracle's help to write this, actually:

SELECT 'select cust_name as cust_location, '''|| table_name ||''' as table_name from ' || table_name || char(13) || chr(10) || 'union all'
FROM all_tab_columns 
WHERE column_name = 'CUST_NAME'

This SQL will generate an output that is the SQL in brackets in the first one; copy it out of the results grid and paste it into the query window

Answer 2

You want all locations regardless of the customer. Some locations are null and must be ignored. I suppose that locations can occur more than once in a table, so I am using DISTINCT :

select distinct cust_name as cust_location, 'tb1' as table_name from tb1 where cust_name is not null
union all
select distinct cust_name as cust_location, 'tb2' as table_name from tbl2 where cust_name is not null
union all
select distinct cust_name as cust_location, 'tb3' as table_name from tbl3 where cust_name is not null