仅当该数据可用时，如何从另一个表将数据附加到串联

编程问答 2022-05-23

问题描述

我有 2 张桌子：

L0INS (ID_INS,Nume_INS)
1 ANB
2 ENEL
3 DIGI

L1AVZ (ID_AVZ,FK_INS,Nume_AVZ)
1 1 APA
2 1 CAN
3 1 HID
4 2 ELE

我想做一个显示以下内容的查询：

Query1 (ID_INS,CONCAT(Nume_INS,Nume_AVZ) )
1 ANB,APA
1 ANB,CAN
1 ANB,HID
2 ENEL,ELE
3 DIGI,n/a

所以它只会将 Name_T2 添加到连接中，如果 Table2 中存在一个条目，它具有 L0INS.ID_INS = L1AVZ.FK_INS

我制作的这个版本确实为每个 Nume_AVZ 附加显示了一个 L0INS 条目，但也显示了一个包含“n/a”的条目。如果还有另一个条目，我想删除“n/a”条目。

SELECT disTINCT     "L0INS"."ID_INS",COALESCE ( "NUME_INS",'n/a' ) || ',' || CASE WHEN "L1AVZ"."FK_INS" = "L0INS"."ID_INS" THEN "L1AVZ"."NUME_AVZ" ELSE 'n/a' END "INS_SELECT",LOWER ( COALESCE ( "NUME_INS",' || CASE WHEN "L1AVZ"."FK_INS" = "L0INS"."ID_INS" THEN "L1AVZ"."NUME_AVZ" ELSE 'n/a' END ) "INS_SEARCH" 

FROM        "L1AVZ","L0INS" 
WHERE   "L0INS"."ID_INS" IS NOT NULL

我感觉 WHERE 部分缺少某些东西，我无法回想。

解决方法

LEFT JOIN 不是更简单吗？

SELECT l1."ID_INS",("NUME_INS" || ',' || OALESCE(l0."NUME_AVZ",'n/a') AS INS_SEARCH"
FROM "L1AVZ" l1 LEFT JOIN
     "L0INS" lO
     ON l1.id_ins = l0.fk_ins;
, 
SELECT L.ID_INS,L.Nume_INS +','+COALESCE(AVZ.Nume_AVZ,'N/A')AS X
FROM L0INS AS L
LEFT JOIN L1AVZ AS AVZ ON L.ID_INS=AVZ.FK_INS
libreoffice-basesqlsql