select * from t1,t2这种写法等价于select * from t1 cross join t2，即生成t1和t2表的笛卡尔积，两个表的所有行都会配对一次。
What’s the difference between comma separated joins and join on syntax in MySQL? – Stack Overflow
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select * from t1,t2这种写法等价于select * from t1 cross join t2，即生成t1和t2表的笛卡尔积，两个表的所有行都会配对一次。
What’s the difference between comma separated joins and join on syntax in MySQL? – Stack Overflow
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