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    <p>Try this:</p> <pre><code>SELECT c1 FROM t1 WHERE substr(c1,1,1) IN ('A','B','C','D', 'E','F','G','H', 'I','J','K','L', 'M','N','O','P', 'Q','R','S','T', 'U','V','W','X', 'Y','Z') AND substr(c1,2,1) IN ('A','B','C','D', 'E','F','G','H', 'I','J','K','L', 'M','N','O','P', 'Q','R','S','T', 'U','V','W','X', 'Y','Z') AND substr(c1,3,1) IN ('1','2','3','4') / </code></pre> <p>If you want also to match lower letters, then apply the upper() function to the 2 first substr(): eg. where upper(substr(c1,1,1)) in ...</p> <p><strong>Performance</strong></p> <p>I tested the Performance of the query with regexp_like and without. As you can see the query without the regexp_like function was 100% faster. (Note. Both querys did a soft-parse)</p> <pre><code>SQL&gt; select count(*) from t1; COUNT(*) ---------- 458752 Elapsed: 00:00:00.02 SQL&gt; set timing off; SQL&gt; select count(*) from t1; COUNT(*) ---------- 458752 SQL&gt; set timing on; SQL&gt; select count(*) from t1 where regexp_like(c1, '[A-Z][A-Z][1-4].*'); COUNT(*) ---------- 65536 Elapsed: 00:00:02.66 SELECT count(*) FROM t1 WHERE substr(c1,1,1) IN ('A','B','C','D', 'E','F','G','H', 'I','J','K','L', 'M','N','O','P', 'Q','R','S','T', 'U','V','W','X', 'Y','Z') AND substr(c1,2,1) IN ('A','B','C','D', 'E','F','G','H', 'I','J','K','L', 'M','N','O','P', 'Q','R','S','T', 'U','V','W','X', 'Y','Z') AND substr(c1,3,1) IN ('1','2','3','4') 18 / COUNT(*) ---------- 65536 Elapsed: 00:00:01.15 SQL&gt; </code></pre> <p><strong>Second Method</strong></p> <p><strong>Get the ascii values of A,Z,1 and 4</strong></p> <pre><code>SQL&gt; select ascii('A') from dual; ASCII('A') ---------- 65 SQL&gt; select ascii('Z') from dual; ASCII('Z') ---------- 90 SQL&gt; select ascii('1') from dual; ASCII('1') ---------- 49 SQL&gt; select ascii('4') from dual; ASCII('4') ---------- 52 </code></pre> <p><strong>Now you can write your statement a lot shorter</strong></p> <pre><code>SELECT count(* ) FROM t1 WHERE ascii(substr(c1,1,1)) BETWEEN 65 AND 90 AND ascii(substr(c1,2,1)) BETWEEN 65 AND 90 AND ascii(substr(c1,3,1)) BETWEEN 49 AND 52 / </code></pre>
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    1. COIf I wanted to match a third character before the number that might or might not be there, what could I do to the second method (ASCII) to allow for this?
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    2. COJust do WHERE substr(c1,1,1) between 'A' and 'Z' ... instead of where ascii(substr(c1,1,1)) BETWEEN 65 AND 90 .
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    3. COI hope that wasn't the extent of your comparison testing. Some of the savings could come from the fact your rows were in memory from the first query. Also, does the ASCII trick work with multibyte character sets? I don't know, just asking.
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