sql性能和高并发的取舍问题

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;

简单的用多表关联是可以的，如果遇到高并发，性能缺陷立即就出来

Answer 1

多表关联并不意味着sql高性能，太复杂的SQL效率损耗并不比外部锁等低，跟高并发也没什么冲突。

建议把语句拆成简单语句，使用锁和补偿机制来保障事务性。