Question

假设我有表A和B，表A包含30行ID，表B包含60行ID，我想通过使用不存在的地方将B.ID插入A.ID。如果表A中不存在B.ID，表B ID将被插入表A中。

INSERT INTO A(
ID)
SELECT ID
FROM B
WHERE NOT EXISTS (Select ID From A WHERE A.ID =  B.ID)

我认为我的子查询存在一些问题。请告诉我如何纠正这个问题。

假设A.ID处于NVARCHAR（200）类型且B.ID处于FLOAT类型。

INSERT INTO A(
ID)
SELECT Cast(Cast(ID as Float)as Nvarchar)
FROM B
WHERE NOT EXISTS (Select ID From A WHERE A.ID =  B.ID)

但仍有错误：将数据类型nvarchar转换为float时出错。

TIA！

Answer 1

使用join代替子查询以获得更好的性能

INSERT INTO A(ID)
SELECT CAST(B.ID AS nvarchar(200))
FROM A RIGHT JOIN B ON A.ID = CAST(B.ID AS NVARCHAR(200)) WHERE A.ID IS NULL

Answer 2

INSERT INTO A(
ID)
SELECT CAST(B.ID AS nvarchar(200))
FROM B
WHERE NOT EXISTS (SELECT 1 FROM A WHERE A.ID =  CAST(B.ID AS nvarchar(200)))