left join on MS SQL 2008 R2
I try to left join two tables. table A contains unique 100 records with field_a_1, field_a_2, field_a_3 and  field_a_1+field_a_2 is unique. table B is multi-million reocrds with multiple fields. field_b_1 is same as field_a_1 and field_b_2 is same as field_a_2. I join two tables together by

select a.*, b.* from a left join b on field_a_1 = field_b_1 and field_a_2 = field_b_2. instead of getting 100 records, I get multi-million records. Do someone know why?

left join on MS SQL 2008 R2
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I try to left join two tables. table A contains unique 100 records with field_a_1, field_a_2, field_a_3 and  field_a_1+field_a_2 is unique. table B is multi-million reocrds with multiple fields. field_b_1 is same as field_a_1 and field_b_2 is same as field_a_2. I join two tables together by

select a.*, b.* from a left join b on field_a_1 = field_b_1 and field_a_2 = field_b_2. instead of getting 100 records, I get multi-million records. Do someone know why?
