sql server - SQL join format - nested inner joins -

i have following sql statement in legacy system i'm refactoring. abbreviated view purposes of question, returning count(*) time being.

select count(*) table1      inner join table2          inner join table3 on table2.key = table3.key , table2.key2 = table3.key2      on table1.differentkey = table3.differentkey 

it generating large number of records , killing system, please explain syntax? , can expressed in other way?

• table1 contains 419 rows
• table2 contains 3374 rows
• table3 contains 28182 rows

edit:

suggested reformat

select count(*) table1      inner join table3           on table1.differentkey = table3.differentkey     inner join table2            on table2.key = table3.key , table2.key2 = table3.key2 

for readability, restructured query... starting apparent top-most level being table1, ties table3, , table3 ties table2. easier follow if follow chain of relationships.

now, answer question. getting large count result of cartesian product. each record in table1 matches in table3 have x * y. then, each match between table3 , table2 have same impact... y * z... result 1 possible id in table 1 can have x * y * z records.

this based on not knowing how normalization or content tables... if key primary key or not..

ex: table 1        diffkey    other val 1          x 1          y 1          z  table 3 diffkey   key    key2  tbl3 other 1         2      6     v 1         2      6     x 1         2      6     y 1         2      6     z  table 2 key    key2   other val 2      6      2      6      b 2      6      c 2      6      d 2      6      e 

so, table 1 joining table 3 result (in scenario) 12 records (each in 1 joined each in 3). then, again times each matched record in table 2 (5 records)... total of 60 ( 3 tbl1 * 4 tbl3 * 5 tbl2 )count returned.

so, now, take , expand based on 1000's of records , see how messed-up structure choke cow (so-to-speak) , kill performance.

select       count(*)          table1           inner join table3             on table1.differentkey = table3.differentkey             inner join table2                on table3.key =table2.key                , table3.key2 = table2.key2