![]() ![]() For example, an index computed on upper(col) would allow the clause WHERE upper(col) = 'JIM' to use an index. This feature can be used to obtain fast access to data based on some transformation of the basic data. Multiple fields can be specified if the index method supports multicolumn indexes.Īn index field can be an expression computed from the values of one or more columns of the table row. The key field(s) for the index are specified as column names, or alternatively as expressions written in parentheses. Indexes are primarily used to enhance database performance (though inappropriate use can result in slower performance). If we are working with a large or busy database, or we just want to have some extra assurances that we will not lose data, I prefer simply adding a new column rather than changing the type of an existing one.CREATE INDEX constructs an index on the specified column(s) of the specified relation, which can be a table or a materialized view. An Alternative to Changing Column Type in PostgreSQL - Adding a New Column InsteadĬhanging a column type is fairly simple, but for a large database with millions of records and a lot of concurrent queries it is also very expensive because of the ACCESS EXCLUSIVE table lock. Honestly it’s hard to know for certain if a table lock will be required by just looking through documentation.įear not, there is an alternative. These commits for not locking when increasing or removing type lengths (eg going from VARCHAR(100) to VARCHAR(255)).This commit for not locking for VARCHAR -> TEXT conversions, and any other conversions that are binary compatible.There are a few hints at exceptions in the PostgreSQL mailing lists, for example: There are some type changes that do not require a lock, but there’s no single place where these are documented (they’re not documented on the ALTER TABLE docs for example), so it’s kind of hard to tell what sort of pain your change will cause. This is crazy slow and expensive, we do not want this to happen to a production database in the middle of the day! When changing the type of a column to a type that has a different internal representation, PostgreSQL will lock the table with an ACCESS EXCLUSIVE lock in order to rewrite the whole table on disk. WARNING: PostgreSQL Column Type Changes Will Lock The Table If you do not use the USING clause, castings can fail and throw errors, like we saw above. When we use the USING clause, we provide an explicit way to transform the values. PostgreSQL will implicitly cast the common values and the constraints to the new data type if you do not use the USING clause, but this doesn’t work for all column type changes. USING Is Not Always Required For Column Type Changes For example we could create a custom function that performs a complex operation and use this instead. ![]() While this example is fabricated, this is a foundation for much more complex and useful transformations. In this simple example we’re converting the value of the title column to be a character count for the original title using a built in PostgreSQL function. Yum.Įxpand your database knowledge with our technical blog.ĪLTER TABLE book ALTER COLUMN title TYPE INTEGER USING ( char_length ( title )) Learn how to use Beekeeper Studio with bite-sized articles. See a list of everything Beekeeper Studio has to offer Work across multiple devices, or share your connections and queries with others. Quickly iterate on a SQL query, view and visualize results, and share with a colleague.Ī spreadsheet like interface to view, navigate, search, and edit your data.Īn easy to use no-code interface to create and alter tables, indexes, foreign keys, and more. ![]() PostgreSQL - Change The Type Of A Column, A Walkthrough With Examples | Beekeeper Studio Beekeeper Studio menuĮxperience a truly modern SQL editor that really sweats the details.
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