SQL 将行值转换为列 headers

Question

我有以下 table:

tableA
+-----------+--------+
| tableA_id |  code  |
+-----------+--------+
|         1 | code A |
|         2 | code B |
|         3 | code A |
|         3 | code C |
|         3 | code B |
|         4 | code A |
|         4 | code C |
|         4 | code B |
|         5 | code A |
|         5 | code C |
|         5 | code B |
+-----------+--------+

我想使用查询将代码 A、代码 B、代码 C 显示为列 headers，然后值将显示 tableA_id 条目是否包含该代码代码字段。所以像这样：

+-----------+------------------------------+
| tableA_id |  code A |  code B  |  code C |
+-----------+------------------------------+
|         1 |   yes   |          |         |
|         2 |         |   yes    |   yes   |
|         3 |   yes   |   yes    |   yes   |

etc...

你能在 SQL 中做到这一点吗？

Answer 1

使用条件聚合（在不同方言之间可移植）：

SELECT tableA_id,
       MAX(CASE WHEN code ='code A' THEN 'yes' END) AS "code A",
       MAX(CASE WHEN code ='code B' THEN 'yes' END) AS "code B",
       MAX(CASE WHEN code ='code C' THEN 'yes' END) AS "code C"
FROM tableA
GROUP BY tableA_id;

SqlFiddleDemo_MySQL SqlFiddleDemo_Postgresql

输出：

╔════════════╦═════════╦═════════╦════════╗
║ tableA_id  ║ code A  ║ code B  ║ code C ║
╠════════════╬═════════╬═════════╬════════╣
║         1  ║ yes     ║ (null)  ║ (null) ║
║         2  ║ (null)  ║ yes     ║ (null) ║
║         3  ║ yes     ║ yes     ║ yes    ║
║         4  ║ yes     ║ yes     ║ yes    ║
║         5  ║ yes     ║ yes     ║ yes    ║
╚════════════╩═════════╩═════════╩════════╝

有很多种可能性（搜索）：

PIVOT            -> SQL Server/Oracle
CROSSTAB         -> Postgresql
SELF OUTER JOIN  -> All
CONDITIONAL AGG  -> All
...

Answer 2

您在 SQL 语法中需要这样的东西

Select *
From Table1
pivot ( Aggregate function For Column Name in ([CodeA], [CodeB] , [CodeC])) as PivotTable

Answer 3

或者，如果您想要一个动态的 SQL 语句，您可以试试下面的方法。您只需更改 table and/or 列的名称。

declare
cursor code is select code, rownum rn, count(*) over (partition by 1 ) as cnt from (select distinct code from test) order by 1;
build_Case clob;
a varchar2(100);
begin

for i in code loop
if i.rn <> i.cnt then
build_case := build_case || CHR(10) || ' max((case when code = ''' || i.code || ''' then ''yes'' else null end)) ' || i.code || ',';
else 
build_case := build_case || CHR(10) || ' max((case when code = ''' || i.code || ''' then ''yes'' else null end)) ' || i.code;
end if;
end loop;

build_case := 'select id,' || build_case || ' from test group by id';
dbms_output.put_line(build_Case);

--execute immediate build_Case;
end;
/

SQL 将行值转换为列 headers

SQL convert row values to column headers

sql

pivot

crosstab