SqlServer UpSert 实现方式（存在则更新，否则插入）

方法1：先查询，根据查询结果判断使用insert或者update

IF EXISTS (SELECT 1 FROM table_A WHERE Id = @Id)
    BEGIN
        UPDATE dbo.table_A
        SET Value = @Value
        WHERE Id = @Id;
    END
ELSE
    BEGIN
        INSERT INTO dbo.table_A (Id, Value)
        VALUES(@Id, @Value)
    END
 

方法2：先更新，根据更新结果影响的条目数判断是否需要插入

UPDATE dbo.table_A
SET Value = @Value
WHERE Id = @Id;
    
IF(@@ROWCOUNT = 0)
BEGIN
    INSERT INTO dbo.table_A (Id, Value)
    VALUES(@Id, @Value)
END
 

方法3：使用MERGE语句，将待upsert的数据作为source，merge到目标表 

MERGE INTO table_A as T
USING (SELECT @Id AS id, @Value AS value ) AS S
ON T.Id = S.id
WHEN MATCHED THEN
    UPDATE SET T.Value = S.value
WHEN NOT MATCHED THEN
    INSERT(Id, Value) VALUES(S.id, S.value);