Oracle PL/SQL查詢不能編譯

Question

誰能告訴我爲什麼這樣不能編譯？我收到一個'缺少的表達式'錯誤：

execute immediate 'select CASE WHEN EXISTS (SELECT 1 from samples where samplecode = :samplecode and auditflag = 0 and ' || varFilterString || ') then 1 else 0 end from DUAL' 
into varResult 
using varSampleCode; 

假設變量都被正確聲明。

TIA

Answer 1

execute immediate 'select count(1) from DUAL 
         where EXISTS 
         (SELECT 1 from samples 
         where samplecode = :sample code 
          and auditflag = 0 
          and ' || varFilterString || ')' 
into varResult 
using varSampleCode;