suppose a field is replaced with"1"at the beginning of"a "and" 2"at the beginning of"1". How to write an update statement is better
I have tried regexp, but then there are a lot of sql statements, and it will be very slow
UPDATE trade SET
transportal="1"
WHERE
transportal REGEXP "^(a)";
is there any way to optimize it
if it is only count statistics, you do not need to do update operation.
I feel that your requirements use the calculated value of the case when expression, and then do count statistics, such as:
select trans_type, count(*)
from (
select case when left(transportal,1) = 'a' then 1 when left(transportal,1) = 'b' then 2 else 0 end as trans_type
from trade
) t
group by trans_typethese should be controlled by the program, and SQL should not do such a thing
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