Table1 t10 (id)

```
id
---
1
2

```

table t11(a1,a2,a3)

```
a1  a2  a3
----------
1   10   a
1   10   b
1   11   b
1   12   c
2   20   d
2   21   e

```

select \* from t10 a,t11 b where a.id = b.a1 
how to display

```
id  a1  a2  a3
--------------
1   1   10  a
1   1   10  b //(not display this row)
1   1   11  b //(not display this row)
1   1   12  c //(not display this row) 
2   2   20  d
2   2   21  e //(not display this row)

```

just get t11's random row

```
maybe display this
id  a1  a2 
---------- 
1   1   11  b
1   1   10  a //(not display this row)
1   1   10  b //(not display this row)
1   1   12  c //(not display this row) 
2   2   20 
2   2   21  //(not display this row) 

```