1.substring_index(字段名，截取标识符，出现的次数)负数是从右边截取
eg:
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update yg_cloud_codes_1 set cg_len=SUBSTRING_INDEX(SUBSTRING_INDEX(cg_codes_tmp,":",2),":",-1)
这样就截取了图中的3000
2.substring(字段名，开始位置，结束位置)
select *, substring(room_id,4) as rid from replay_user_tbl order by id desc limit 1,10
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3.left(字段名，结束位置)
select *, left(room_id,4) as rid from replay_user_tbl order by id desc limit 1,10
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find_in_set
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5.group操作后，拼接指定字段的数据
select tax_type,GROUP_CONCAT(group_id SEPARATOR ',' ) groupids FROM game_tax_tbl GROUP BY tax_type;
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