sql - 将限制设置为 array_agg()

Question

我有以下 Postgres 查询:

SELECT array_agg("Esns".id ) 
FROM public."Esns", 
     public."PurchaseOrderItems" 
WHERE 
    "Esns"."PurchaseOrderItemId" = "PurchaseOrderItems".id 
    AND "PurchaseOrderItems"."GradeId"=2 
LIMIT 2;

限制会影响行数。我希望它将 array_agg() 限制为 2 个项目。以下查询有效，但我得到的输出包含引号中的每个条目:

SELECT array_agg ("temp")  
FROM (
    SELECT "Esns".id 
    FROM public."Esns", 
         public."PurchaseOrderItems" 
    WHERE 
        "Esns"."PurchaseOrderItemId" = "PurchaseOrderItems".id 
        AND "PurchaseOrderItems"."GradeId"=2 
    LIMIT 4
) as "temp" ;

这给了我以下输出

{(13),(14),(15),(12)}

有什么想法吗？

Answer 1

select id[1], id[2]
from (
    SELECT array_agg("Esns".id ) as id
    FROM public."Esns", 
         public."PurchaseOrderItems" 
    WHERE 
        "Esns"."PurchaseOrderItemId" = "PurchaseOrderItems".id 
        AND "PurchaseOrderItems"."GradeId"=2 
) s

或者如果你想要输出为数组，你可以 slice它:

SELECT (array_agg("Esns".id ))[1:2] as id_array
FROM public."Esns", 
     public."PurchaseOrderItems" 
WHERE 
    "Esns"."PurchaseOrderItemId" = "PurchaseOrderItems".id 
    AND "PurchaseOrderItems"."GradeId"=2