如何仅在该数据可用时将来自另一个 table 的数据附加到串联

Question

我有 2 个表：

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

我想查询显示以下内容：

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

所以如果 Table2 中存在具有 L0INS.ID_INS = L1AVZ.FK_INS

的条目，它只会将 Name_T2 添加到串联中

我制作的这个版本确实为每个 Nume_AVZ 附加项显示了一个 L0INS 条目，但也显示了一个包含 'n/a' 的附加项。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", 'n/a' ) || ', ' || 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，我无法理解。

Answer 1

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;

Answer 2

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

如何仅在该数据可用时将来自另一个 table 的数据附加到串联

How to append data to a concatenation, from another table, only if that data is available

sql

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