SELECT A.*, B.* FROM A LEFT OUTER JOIN
B ON A.emp_id = B.emp_id
WHERE B.emp_fname = @emp_fnameSELECT A.*, C.* FROM A LEFT OUTER JOIN
(SELECT * FROM B WHERE B.emp_fname = @emp_fname) C ON A.emp_id = C.emp_id假设表A的数据量较大,请问以上两条SQL语句哪个效率比较高呀,为什么?
B ON A.emp_id = B.emp_id
WHERE B.emp_fname = @emp_fnameSELECT A.*, C.* FROM A LEFT OUTER JOIN
(SELECT * FROM B WHERE B.emp_fname = @emp_fname) C ON A.emp_id = C.emp_id假设表A的数据量较大,请问以上两条SQL语句哪个效率比较高呀,为什么?
B ON A.emp_id = B.emp_id
WHERE B.emp_fname = @emp_fname
(SELECT * FROM B WHERE B.emp_fname = @emp_fname) C ON A.emp_id = C.emp_id
这种
子查询效率高