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Mysql column with null values - what are the space requirements? -
i have table quite lot entries. need additional column integer value or null. thing few rows have field populated.
so wonder whether better create seperate table link entries in 1:1 relation.
i know 1 integer entry takes 4 bytes in mysql/myisam. if have column set allow null values, , 100 of 100 000 rows have field populated, rest still consume 4 bytes every null value?
or mysql intelligent enough set value populated , regard null, nothing set?
this depends on row_format value give when create table.
before version 5.0.3, default format set "redundant" : fixed-length field use same space, if it's value null.
starting version 5.0.3, value set "compact" : null values never use space in database.
you can alter table sure use correct format :
alter table ... row_format=compact
more details here : http://dev.mysql.com/doc/refman/5.1/en/data-size.html
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