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How to use case in insert into select statement?

Posted on 2014-11-20
Medium Priority
Last Modified: 2014-11-20
Dear Experts,

Is below statement is true or can you offer an alternative?

Table TA (x,y,z,t)
Table TB (a,b,c,d)

insert into TA (x,y,z,t) select a,b,c,(case when c=1 then 'XXX' else TB.d end)

Please be careful that if c=1 then assign constant value 'XXX' else assign value of column d)

Question by:GurcanK
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LVL 74

Expert Comment

ID: 40455218
insert into TA (x,y,z,t) select a,b,c,(case when c=1 then 'XXX' else d end) from tb
LVL 77

Assisted Solution

by:slightwv (䄆 Netminder)
slightwv (䄆 Netminder) earned 1000 total points
ID: 40455221
>>insert into TA (x,y,z,t) select a,b,c,(case when c=1 then 'XXX' else TB.d end)

you are missing the FROM TB after the select.

Just like the last two questions:  Looks good.

Just set up some test tables and try it.
LVL 74

Accepted Solution

sdstuber earned 1000 total points
ID: 40455224
insert into TA (x,y,z,t) select a,b,c, decode(c,1,'XXX',d) from tb
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LVL 77

Assisted Solution

by:slightwv (䄆 Netminder)
slightwv (䄆 Netminder) earned 1000 total points
ID: 40455230
Missed something:
then 'XXX' else TB.d

Since 'XXX' is a string, TB.d will need to be a varcahr2 or similar string variable.  if it is a number or a date, you will likely get an error.  You will need to convert TB.d to a string datattype by using TO_CHAR and the appropriate formatting.
LVL 74

Expert Comment

ID: 40455241
actually, since 'XXX' is a string, and it's the first return result in the CASE, it's determining the data type of the rest of the case results,  so anything else will be implicitly converted to text (char)

so, you probably won't get an error, but you might get funny results if your data converts into a format you don't want.

So, TO_CHAR with an explicit format for non-text data is a good idea.

Same applies to the DECODE alternative
LVL 77

Expert Comment

by:slightwv (䄆 Netminder)
ID: 40455246

SQL> select case when 1=1 then 'XXX' else 1 end from dual
ERROR at line 1:
ORA-00932: inconsistent datatypes: expected CHAR got NUMBER

SQL> select case when 1=1 then 'XXX' else to_char(1) end from dual;

Author Comment

ID: 40455256
Thanks all, fortunately data-types are the same.
LVL 74

Expert Comment

ID: 40455267
interesting - I stand corrected.  Thanks!

I know I've seen the first element determine data types before.  Maybe it was a bug in older versions.

Does work with decode though


and thanks again!

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