What does =* mean?

Question

I'm trying to trace some SQL in Microsoft Server. I came across a join that is using a convention unfamiliar to me. What does "=*" mean?

WHERE table1.yr =* table2.yr -1 

Answer 1

This:

WHERE t.column =* s.column 

...is old TSQL (pre SQL Server 2005) outer join syntax, and is not an ANSI JOIN.

Reference: SQL Server 2005 Outer Join Gotcha

Answer 2

I believe that is old syntax indicating an outer join condition from table1 to table2

Old style:

SELECT * FROM table1, table2 WHERE table1.yr =* table2.yr -1 

New style (SQL92):

SELECT * FROM table2  LEFT OUTER JOIN table1 ON table1.yr = table2.yr - 1