报表统计 sql 字段的值存多个值，用逗号分隔，在sql统计的时候语句如何写？

certificate在数据库的值有可能是c1，c2，c3，c4 还有可能是c1，c2等等，
"sum(decode(a.certificate,'c1',1,0)) as certificate_c1, "

如何统计出每种证书的所有数量？

SELECT certificate,COUNT(certificate) FROM a GROUP BY certificate

loveexception

select sum( case when LOCATE(a.certificate, ‘c1‘) > 0 then 1 else 0 ) as c1 from

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