Question

I am having two tables like this.Both are separate tables

AccountNo       User         Name
----------------------------------
 1               U            a
 2               U            b
 3               U            c

And another table contains the following structure

 TempAccountNo       Mycolumn    AccountNo     
------------------------------------------
 4               X                2341
 5               Y                 2
 6               Z                2568

I need to select the AccountNo or TempAccountNo,Mycolumn From table II and the condition is

If (tableII.AccountNo not in table I)

   I need to choose `TempAccountNo from table II`

else
  I need to choose `AccountNo from table II`

How can I achieve this.

Answer 1

SELECT IF(
    t1.AccountNo IS NULL, -- condition
    t2.TempAccountNo,     -- true branch
    t2.AccountNo          -- false branch
  ) AS optional_field
FROM table2 t2
  LEFT JOIN t1 ON t1.AccountNo = t2.AccountNo