案例表达式在 sql 查询中无法正常工作

Question

I want to concat columns of supplier table with comma separator and put it into an alias field named 'contact'. I have used cases for checking null values. Suppose if contact_number2 is null then contact_number3 will be in alias field and vice versa. Here is my query

SELECT supplier_Name, supplier_Address, supplier_reference, contact_Number1,
       contact_number2, contact_number3,
      (case when contact_number2 is null then contact_number3 
            when contact_number3 is null then contact_number2 
            when contact_number3 is null and contact_number2 is null then 0
         -- when contact_number2 is not null and contact_number3 is not null then  CONCAT(CONCAT(contact_number2,','), contact_number3)
       end) as contact
FROM SUPPLIER

If I use the fourth condition then it works but if I use multiple condition then it doesn't work.The error is ORA-00932: inconsistent datatypes: expected NUMBER got CHAR 00932. 00000 - "inconsistent datatypes: expected %s got %s"

Answer 1

The third case is expecting a VARCHAR and you are providing an INT because of which it is returning an error. Change was that I replaced 0 with '0'. Try this:

SELECT supplier_Name,supplier_Address,supplier_reference,contact_Number1,contact_number2, contact_number3,   

  (case 
   when contact_number2 is null then contact_number3 
    when contact_number3 is null then contact_number2 
    when contact_number3 is null and contact_number2 is null then '0'
  when contact_number2 is not null and contact_number3 is not null then  CONCAT(CONCAT(contact_number2,','), contact_number3)
   end)

   as contact

Answer 2

I think you're after something like this:

select supplier_name,
       supplier_address,
       supplier_reference,
       contact_number1,
       contact_number2,
       contact_number3,
       case when contact_number2 is not null and contact_number3 is not null then contact_number2||','||contact_number3
            when contact_number3 is null and contact_number2 is null then '0'
            when contact_number2 is null then to_char(contact_number3)
            when contact_number3 is null then to_char(contact_number2)
       end as contact
from   supplier;

Note that case expressions stop at the first condition that is met, so you should make sure that the conditions are in the right order. (Eg. in my query, by the time you get to the "when contact_number2 is null then contact_number3" we already know that contact_number3 can't be null due to the previous condition.)

Also, I have converted your CONCAT into the much more common (and more flexible) || form. With CONCAT , you can only concatenate 2 things at a time, whereas you can have multiple || s to join various strings together.

The reason why you got the error you did is because when you concatenate two numbers together (especially when you add a comma into the mix!) the result will be a string. CASE expressions like you to use the same datatype for the result of each condition.

Answer 3

You have to cast numeric data as character before concat.

A case expression's all return values must be type compatible:

SELECT supplier_Name, supplier_Address, supplier_reference, contact_Number1,
       contact_number2, contact_number3,
       case when contact_number2 is not null and contact_number3 is not null
                then CONCAT(CONCAT(cast(contact_number2 as varchar(15)),','),
                            cast(contact_number3 as varchar(15)))
            else cast(coalesce(contact_number2, contact_number3, 0) as varchar(15))
       end as contact
FROM SUPPLIER

Answer 4

Use this

  SELECT supplier_Name, supplier_Address, supplier_reference, contact_Number1,
     contact_number2, contact_number3,
     case when contact_number2 is null then contact_number3 
          when contact_number3 is null then contact_number2 
          when contact_number3 is null and contact_number2 is null then '0'
          when contact_number2 is not null and contact_number3 is not null then contact_number2||','||contact_number3
     end as contact
  FROM SUPPLIER