1、问题来源在使用postgresql 函数 crosstab 进行行转列时遇到的这个问题，在元数据中使用了sum函数，crosstab 无法确定返回的数据类型

出现错误写法如下：

select * from crosstab('select t1.createtime::date ,t1.property ,sum(t1.propertyvalue)
from property_value t1
where 1=1
group by t1.createtime,t1.property
order by t1.createtime desc ,t1.property')
as ct (createTime date,"chinese" int4,"english" int4,"math" int4,"music" int4,"sports" int4)

执行sql出现如下错误：SQL 错误 [42601]: 错误: return and sql tuple descriptions are incompatible

2、解决方法，正确写法如下，将sum 结果 通过 cast 函数转换一下数据类型

select * from crosstab('select t1.createtime::date ,t1.property ,cast(sum(t1.propertyvalue) as int4)
from property_value t1
where 1=1
group by t1.createtime,t1.property
order by t1.createtime desc ,t1.property')
as ct (createTime date,"chinese" int4,"english" int4,"math" int4,"music" int4,"sports" int4)

3、总结，cast的用法

3.1、字符串（varchar）转换数值（int4）

select cast('1' as int4)

3.2、时间转换（timestamp）转换日期（date）

select cast('2020-10-10 10:43:54' as date)

3.3、数值（int4）转换字符串（ varchar）

select cast(1 as varchar)