Hello, The +4 is for the overhead of a varchar field. Using ALTER TABLE <table> ALTER <field> TYPE VARCHAR(<newsize>) to change the size requires scanning the entire table. For large tables, this will be much slower than the pg_attribute query. Both will get the job done. af300wsm@xxxxxxxxx wrote: > Hello, > > In this case, I don't have to alter the definition to the extent of > changing the data type, but rather to change the length of a varchar > field/column. I found the following from a past posting to one of the > PostgreSQL user lists that does work, but I'd like something a bit more > elegant and wanted to find out if anything better exists in PostgreSQL > 8.1.3 before I went and altered more than my test DB. Here is what I > found (note that the person he was responding to wanted to bring his > varchar field from 10 to 75 characters, in light of this, why is 4 > added to 75?): > > update pg_attribute set atttypmod = 75 + 4 > where attname = 'columnname' and > attrelid = (select oid from pg_class where relname = 'tablename'); > > The above comes from a posting made in Oct. of 2001. Also, I found > this posting to this newsgroup in Oct. of last year mentioning: > > <quote> > > Am I right in thinking that altering a column from varchar(n) to > > varchar(n+m) requires each tuple to be visited? > > Yes. Doing otherwise would require an unreasonable amount of > data-type-specific knowledge hardwired into ALTER COLUMN TYPE. > </quote> > > What is this talking about and how does it apply to what I need to do? > > Thanks, > Andy
