WITH value_comparison AS (
    SELECT
        col1, col2, col3, col4, col5, col6,
        -- 判断 col1 和 col2 的差值是否在正负30%以内
        CASE 
            WHEN col2 IS NOT NULL AND col1 IS NOT NULL 
                THEN ABS(col1 - col2) / col2 <= 0.3
            ELSE NULL 
        END AS use_col1_over_col2,
        
        -- 判断 col1 和 col3 的差值是否在正负30%以内
        CASE 
            WHEN col3 IS NOT NULL AND col1 IS NOT NULL 
                THEN ABS(col1 - col3) / col3 <= 0.3
            ELSE NULL 
        END AS use_col1_over_col3,
        
        -- 判断 col1 和 col4 的差值是否在正负30%以内
        CASE 
            WHEN col4 IS NOT NULL AND col1 IS NOT NULL 
                THEN ABS(col1 - col4) / col4 <= 0.3
            ELSE NULL 
        END AS use_col1_over_col4,
        
        -- 判断 col1 和 col5 的差值是否在正负30%以内
        CASE 
            WHEN col5 IS NOT NULL AND col1 IS NOT NULL 
                THEN ABS(col1 - col5) / col5 <= 0.3
            ELSE NULL 
        END AS use_col1_over_col5,
        
        -- 判断 col1 和 col6 的差值是否在正负30%以内
        CASE 
            WHEN col6 IS NOT NULL AND col1 IS NOT NULL 
                THEN ABS(col1 - col6) / col6 <= 0.3
            ELSE NULL 
        END AS use_col1_over_col6
    FROM your_table
)
SELECT
    CASE
        -- 若 col1 不为空，优先处理 col1
        WHEN col1 IS NOT NULL THEN
            CASE
                WHEN col2 IS NOT NULL THEN
                    CASE 
                        WHEN use_col1_over_col2 THEN col1 
                        ELSE col2 
                    END
                WHEN col3 IS NOT NULL THEN
                    CASE 
                        WHEN use_col1_over_col3 THEN col1 
                        ELSE col3 
                    END
                WHEN col4 IS NOT NULL THEN
                    CASE 
                        WHEN use_col1_over_col4 THEN col1 
                        ELSE col4 
                    END
                WHEN col5 IS NOT NULL THEN
                    CASE 
                        WHEN use_col1_over_col5 THEN col1 
                        ELSE col5 
                    END
                WHEN col6 IS NOT NULL THEN
                    CASE 
                        WHEN use_col1_over_col6 THEN col1 
                        ELSE col6 
                    END
                ELSE col1 -- 若只有 col1 不为空，直接使用 col1
            END
        -- 若 col1 为空，则依次检查后续列
        WHEN col2 IS NOT NULL THEN col2
        WHEN col3 IS NOT NULL THEN col3
        WHEN col4 IS NOT NULL THEN col4
        WHEN col5 IS NOT NULL THEN col5
        ELSE col6 -- 若所有列都为空，返回 col6（可能为 NULL）
    END AS final_value
FROM value_comparison;