1 decode

It changes the value of an expression if it is equal to one of the searched values.

<decode
    when='when'
    cond='cond'
    then='then'
    else='else'
/>
Example
Copy
<select>
   <columns>
      <decode when='deptno' cond='10' then='ACCOUNTING' else='NONE'/>
   </columns>
   <from table='test'/>
</select>
 

2 nvl

This tag is used to convert an expression that evaluates as NULL to the value specified.

<nvl>
    <expresion /> *
</nvl>
Example

If 'salario' is null, the value 0 must be returned.

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<select>
   <columns>
      <nvl>salario,0</nvl>
   </columns>
   <from table='empleados'/>
</select>