xdazzの回答の助けを借りて、私はいくつかの変更を行い、最終的に回答を得ました...
SELECT
myWord,
LEAST (
if (Locate('0',myWord) >0,Locate('0',myWord),999),
if (Locate('1',myWord) >0,Locate('1',myWord),999),
if (Locate('2',myWord) >0,Locate('2',myWord),999),
if (Locate('3',myWord) >0,Locate('3',myWord),999),
if (Locate('4',myWord) >0,Locate('4',myWord),999),
if (Locate('5',myWord) >0,Locate('5',myWord),999),
if (Locate('6',myWord) >0,Locate('6',myWord),999),
if (Locate('7',myWord) >0,Locate('7',myWord),999),
if (Locate('8',myWord) >0,Locate('8',myWord),999),
if (Locate('9',myWord) >0,Locate('9',myWord),999)
) as myPos
FROM myTable;