java - sql效能和高並發的取捨問題

Question

SELECT

        S.carOwnerID ,
        S.name,
        S.mobile,
        S.coopName,
        S.VIN,
        s.policyNO,
        S.effectiveDate,
        S.expiryDate,
        s.plateNo,
        (
            CASE
            WHEN s.num > 1 THEN
                1
            WHEN s.num = 1 THEN
                0
            END
        ) AS carState
    FROM
        (
            SELECT
                c.carOwnerID,
                c.name,
                c.mobile,
                c.coopName,
                c.VIN,
                p.policyNO,
                p.effectiveDate,
                p.expiryDate,
                c.plateNo,
                count(p.PlateNo) AS num
            FROM
                customer C
            LEFT JOIN policy P ON C.carOwnerID = P.carOwnerID
            WHERE
                date_add(
                    P.createTime,
                    INTERVAL 11.5 HOUR
                ) > NOW()
    
    ) s
    WHERE
        s.num > 0;

簡單的用多表關聯是可以的，如果遇到高並發，效能缺陷立即就出來

Answer 1

多表關聯並不代表sql高效能，太複雜的SQL效率損耗也不比外部鎖等低，跟高並發也沒什麼衝突。

建議把語句拆成簡單語句，使用鎖和補償機制來保障事務性。