目标：sql将多行数据转化成一行数据
涉及语法：decode,nvl，left join ,子查询。
--nvl(a,b)->如果a不存在就显示b,否则显示a
--decode，oracle独有的if,else;eg：decode(a,1,2);如果a=1,就返回2
2 SELECT 3 A.EMPLOYEE_GID, 4 A.EVALUATE_YEAR, 5 DECODE(NVL(A.EVALUATION_STEP, 0), 0, 0, 1, 1) AS STEP1, 6 DECODE(NVL(B.EVALUATION_STEP, 0), 0, 0, 2, 1) AS STEP2, 7 DECODE(NVL(C.EVALUATION_STEP, 0), 0, 0, 3, 1) AS STEP3, 8 ( NVL(C.EVALUATION_STEP, B.EVALUATION_STEP) 9 || DECODE(NVL(A.EVALUATION_STEP, 0), 0, 0, 1, 1) 10 || DECODE(NVL(B.EVALUATION_STEP, 0), 0, 0, 2, 1) ) AS COMBINE_STEP, 11 DECODE((NVL(C.EVALUATION_STEP, B.EVALUATION_STEP) 12 || DECODE(NVL(A.EVALUATION_STEP, 0), 0, 0, 1, 1) 13 || DECODE(NVL(B.EVALUATION_STEP, 0), 0, 0, 2, 1)), 311, 2, 301, 2, 300, 0, 310, 1, 211, 2, 201, 2) AS WITHDRAW_STEP14 , 15 DECODE((NVL(C.EVALUATION_STEP, B.EVALUATION_STEP) 16 || DECODE(NVL(A.EVALUATION_STEP, 0), 0, 0, 1, 1) 17 || DECODE(NVL(B.EVALUATION_STEP, 0), 0, 0, 2, 1)), 311, 1, 301, 0, 300, 0, 310, 0, 211, 1, 201, 0) AS WITHDRAW_COLOR18 FROM 19 ( 20 SELECT 21 * 22 FROM 23 T_EVALUATION A 24 WHERE 25 EVALUATION_STEP = 1 26 ) A 27 LEFT JOIN ( 28 SELECT 29 * 30 FROM 31 T_EVALUATION A 32 WHERE 33 EVALUATION_STEP = 2 34 ) B ON A.EVALUATE_YEAR = B.EVALUATE_YEAR 35 AND A.EMPLOYEE_GID = B.EMPLOYEE_GID 36 LEFT JOIN ( 37 SELECT 38 * 39 FROM 40 T_EVALUATION A 41 WHERE 42 EVALUATION_STEP = 3 43 ) C ON A.EVALUATE_YEAR = C.EVALUATE_YEAR 44 AND A.EMPLOYEE_GID = C.EMPLOYEE_GID 45 WHERE 46 A.EVALUATE_YEAR = ( 47 SELECT 48 VALUE 49 FROM 50 S_SYSTEM_CONFIG 51 WHERE 52 KEY = 'CURRENT_FINANCE_YEAR' 53 AND ENABLE = 1 54 ) 55 AND ( C.EVALUATION_STEP IS NOT NULL 56 OR B.EVALUATION_STEP IS NOT NULL )