select a.ename, a.mgr, a.sal, b.deptno
from emp a, dept b
where a.deptno = b.deptno
and b.deptno in ('ACCOUNTING', 'RESEARCH', 'SALES', 'OPERATIONS')
AND 1=1;
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where t1.id=t2.id and 1=1 and where t1.name=t2.name
where t1.id=t2.id and where t1.name=t2.name
where t1.id=t2.id and where t1.name=t2.name and 1=1
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前面确定结果?where t1.id=t2.id and 1=1 and where t1.name=t2.name //那这个情况t1.id=t2.id不成立,后面,t1.name=t2.name就不执行聊吗?大哥