[improvement](ctas) use string type for varchar/char/string #14382
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…4382) When executing create table as select stmt, the varchar/char/string type of column in created table will be unified to string type. Because when select from external table (mysql/pg, etc), the length of varchar in external database is calculated by "char" length, not "byte" length. So if there is a column with varchar(10) in external table, then there will be a same varchar(10) in created table. But the byte length of data in external table may be larger than 10, causing failure of CTAS. Change to string will not impact performance of the capacity of disk storage. And notice that if a string type column is the first column, it will be changed to varchar(65535), because we do not allow string type column as sort key column.
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Proposed changes
Issue Number: close #xxx
Problem summary
When executing
create table as selectstmt,the varchar/char/string type of column in created table will be unified to
stringtype.Because when select from external table (mysql/pg, etc), the length of varchar in external database
is calculated by "char" length, not "byte" length.
So if there is a column with
varchar(10)in external table, then there will be a samevarchar(10)in created table. But the byte length of data in external table may be larger than 10, causing failure of CTAS.
Change to string will not impact performance of the capacity of disk storage.
And notice that if a string type column is the first column, it will be changed to
varchar(65535),because we do not allow string type column as sort key column.
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Further comments
If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...