Now I have one table, let's say table PROPERTY, which have 2 columns called A and B, 

```
A B     PIVOT  
1 dog   T  
2 cat   T  
1 chien F  
1 gou   F  
2 chat  F  
2 miao  F  

```

Now I want to add one column C, whose content is based on A and B, and is indexed by 1. that's to say, 

```
A B     C  
1 dog   dog  
2 cat   cat  
1 chien dog  
1 gou   dog  
2 chat  cat  
2 miao  cat 

```

How can I do this? This is a large table(200k rows)

I was thinking about:

```
UPDATE PROPERTY a SET C= 
     (select min(b.B) from CFG_DIM_PROPERTY b where 
          b.A=  a.A and b.PIVOT= 'T')

```

However, this sql has taken too much time. Do you smart guys know other ways? And some indications about how you thought of it?