mysql usage of case..when ..then..else..end as ..

1. Example 1

SELECT CASE main_xm_sam31 WHEN '02' THEN 2 ELSE 1 END AS SPDJ FROM SR_MAIN_BG A WHERE A.PK_SR_MAIN = '1162275825622593536' AND (SYS_SPDJ = 0 OR SYS_SPDJ = -1)