sfdsaf, Oracle - rextester

Language: Layout:

WITH test_data AS 
(
        SELECT 'alex.hales@gmail.com' AS email FROM dual
        UNION ALL
        SELECT 'Joeroot.eng@yahoo.co.in' FROM dual
        UNION ALL
        SELECT 't.e.s.t.ex.ampl.e@do.ma.i.com' FROM dual
        UNION ALL
        SELECT 't1@z.a' FROM dual
)
SELECT z.email,
    CASE WHEN INSTR(part1_masked, '*',1, 5) > 0 
          THEN SUBSTR(part1_masked,1,INSTR(part1_masked, '*',1, 5)) 
               || SUBSTR(part1, INSTR(part1_masked, '*',1, 5)+1)
            ELSE part1_masked
    END || '@' 
    || SUBSTR(part2_masked,1,INSTR(part2_masked, '.',-1)-1)
    || SUBSTR(part2,INSTR(part2, '.',-1,1)) AS masked_email 
FROM
(
    SELECT 
      email
     ,SUBSTR(t.email, 1, INSTR(t.email, '@')-1) AS part1
     ,SUBSTR(t.email,INSTR(t.email, '@')+1) AS part2
     ,regexp_replace(SUBSTR(t.email, 1, INSTR(t.email, '@')-1),
                            '[[:alnum:]]', '*') AS part1_masked
     ,regexp_replace(SUBSTR(t.email,INSTR(t.email, '@')+1),
                            '[[:alnum:]]', '*') AS part2_masked
    FROM test_data t    
) z


absolute service time: 0,85 sec