SELECT B.D,B.E,A.A,B.G FROM A表 A  LEFT JOIN B表 B on A.A=B.F

---------

with t1 as(

SELECT '2024-01' [A] UNION ALL

SELECT '2024-02' [A] UNION ALL

SELECT '2024-03' [A] UNION ALL

SELECT '2024-04' [A] UNION ALL

SELECT '2024-05' [A] UNION ALL

SELECT '2024-06' [A] UNION ALL

SELECT '2024-07' [A] UNION ALL

SELECT '2024-08' [A] UNION ALL

SELECT '2024-09' [A] UNION ALL

SELECT '2024-10' [A] UNION ALL

SELECT '2024-11' [A] UNION ALL

SELECT '2024-12' [A] 

),

T2 AS (

SELECT '张三' [A],'数学' [B],'2024-01' [C],'100' [D] UNION ALL

SELECT '张三' [A],'语文' [B],'2024-01' [C],'99' [D] UNION ALL

SELECT '张三' [A],'数学' [B],'2024-05' [C],'300' [D] UNION ALL

SELECT '张三' [A],'语文' [B],'2024-05' [C],'500' [D]

)

SELECT distinct T3.A,T3.B,T3.C,T2.D FROM

 (

SELECT T2.A,T2.B,T1.A [C] FROM T2 cross JOIN T1 )

T3 LEFT JOIN T2 ON T3.C=T2.C AND T3.B=T2.B 

两个表用笛卡尔集关联