Define variable in Oracle SQL developer
<p>I'm trying to define standard values in variables in ORACLE SQL Developer, but it keeps asking me to enter a value. How can I avoid that and put as default value for v_mode ='X1','X2' and set COB_DATE to 14 July so that there is NO popup?</p>

<pre><code> variable   COB_DATE date
 variable   v_mode varchar(20);
 exec :COB_DATE := '14-JUL-2016';
 exec :v_mode := 'MAG';

select * 
    FROM DF_RISK_SIT2_OWNER.recon_ts_rs
    WHERE SRC_HUB = 'DBRS'
    AND TRD_SRC_SYS in :v_mode 
    AND DSET_COB_DT = :COB_DATE
</code></pre>

<p>but I get the error: Bind Variable "COB_DATE" is NOT DECLARED</p>