将多条记录合并成一行

Question

我试图让两条单独的记录显示在一行上，但不断收到多行空值。我想，如果我按 Test_Date 分组，我就可以在每个测试日期得到一行，分数在一行上，但正如你所看到的，这对我来说行不通。

如何将这两行合并为一行，在阅读分数旁边显示数学分数？

SELECT st.test_date, t.name, decode(ts.name,'Mathematics', sts.numscore) as Mathematics,
decode(ts.name, 'Reading', sts.numscore) as Reading
FROM studenttestscore sts
     JOIN studenttest st ON sts.studenttestid = st.id
     JOIN testscore ts ON sts.testscoreid = ts.id
     JOIN test t on ts.testid = t.id
     JOIN students s ON s.id = st.studentid
WHERE t.id IN (601, 602, 603)
     AND s.student_number = '108156'
GROUP BY st.test_date, t.name, 
         decode(ts.name,'Mathematics', sts.numscore),
         decode(ts.name, 'Reading', sts.numscore)
ORDER BY st.test_date

--- CURRENT OUTPUT ---

Test_Date    Name        Mathematics    Reading
29-AUG-13    MAP FALL            227     (null)
29-AUG-13    MAP FALL         (null)        213
22-JAN-14    MAP WINTER          231     (null)
22-JAN-14    MAP WINTER       (null)        229
05-MAY-14    MAP SPRING          238     (null)
05-MAY-14    MAP SPRING       (null)        233

--- DESIRED OUTPUT ---

Test_Date    Name        Mathematics    Reading
29-AUG-13    MAP FALL            227        213
22-JAN-14    MAP WINTER          231        229
05-MAY-14    MAP SPRING          238        233

Answer 1

您似乎希望日期和姓名同名，所以只将它们包含在 GROUP BY 中。其余使用聚合函数：

SELECT st.test_date, t.name,
       MAX(CASE WHEN ts.name = 'Mathematics' THEN sts.numscore END) as Mathematics,
       MAX(CASE WHEN ts.name = 'Reading' THEN sts.numscore END) as Reading
FROM studenttestscore sts JOIN
     studenttest st
     ON sts.studenttestid = st.id JOIN
     testscore ts
     ON sts.testscoreid = ts.id JOIN
     test t
     ON ts.testid = t.id JOIN
     students s
     ON s.id = st.studentid
WHERE t.id IN (601, 602, 603) AND s.student_number = '108156'
GROUP BY st.test_date, t.name, 
ORDER BY st.test_date;

我还将 decode() 替换为 CASE，这是在表达式中表达条件的 ANSI 标准形式。

Answer 2

您必须使用 Aggergate MAX() 并按名称和测试日期分组才能获得所需的结果

Sample SQL Fiddle

select t.test_date, 
        t.name, max(Mathematics) as Mathematics,
        max(Reading) as Reading 
from t
GROUP BY t.test_date, t.name
ORDER BY t.test_date;

将多条记录合并成一行

Merge multiple records in single row

sql

oracle

null

group-by

oracle11g