oceanbase

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drop table if exists t1,t2,t5,t6;
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CREATE TABLE t1 (
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pk int primary key,
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id int,
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gender varchar(1)
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);
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CREATE TABLE t2 (
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user_id int primary key,
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birthday datetime
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);
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insert into t1 values (1, NULL, 'M'), (2, 1, 'M'), (3, 2, 'F'),(4, 3, 'F'),(5, 4, 'F'),(6, 5, 'M');
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insert into t2 values (1, '2002-06-09 00:00:00'),(2, '2002-06-09 00:00:00'),(100, '2002-06-09 00:00:00'),
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(3, '2002-06-09 00:00:00'),(4, '2002-06-09 00:00:00');
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select  id,gender,user_id from  t1,t2  where t2.user_id=t1.id;
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id	gender	user_id
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1	M	1
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2	F	2
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3	F	3
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4	F	4
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create table t5(a int);
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create table t6(a int);
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insert into t5 values (null), (null);
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insert into t6 values (null), (null);
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select * from t5, t6 where t5.a <=> t6.a;
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a	a
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NULL	NULL
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NULL	NULL
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NULL	NULL
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NULL	NULL
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drop table t1,t2,t5,t6;
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