SELECT goods_id,count(*) FROM t GROUP BY goods_id;
默认情况下,MySQL对所有GROUP BY col1,col2…的字段进行排序。如果查询包括GROUP BY,想要避免排序结果的消耗,则可以指定ORDER BY NULL禁止排序。
建议修改成
SELECT goods_id,count(*) FROM t GROUP BY goods_id ORDER BY NULL;
RAND随机优化
SELECT * FROM t1 WHERE 1=1 ORDER BY RAND() LIMIT 4;
MySQL不支持函数索引,会导致全表扫描
建议修改成
SELECT * FROM t1 WHERE id >= CEIL(RAND()*1000) LIMIT 4;
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mysql :RAND和GROUP BY优化
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