4/14/2023 0 Comments Alter table add columnSELECT groupArray ( x ), groupArray ( s ) FROM ( select x, s from tmp order by x ) ![]() numbers LIMIT 5 ĪLTER TABLE tmp ADD COLUMN s String MATERIALIZED toString ( x ) This approach allows us to complete the ALTER query instantly, without increasing the volume of old data.ĬREATE TABLE tmp ( x Int64 ) ENGINE = MergeTree ( ) ORDER BY tuple ( ) PARTITION BY tuple ( ) ![]() ![]() The column appears on the disk after merging data parts (see MergeTree). If the data is missing for a column when reading from the table, it is filled in with default values (by performing the default expression if there is one, or using zeros or empty strings). The data does not appear on the disk after ALTER. For a chain of actions, name_after can be the name of a column that is added in one of the previous actions.Īdding a column just changes the table structure, without performing any actions with data. Otherwise, the column is added to the end of the table. If you want to add a column to the beginning of the table use the FIRST clause. If you specify AFTER name_after (the name of another column), the column is added after the specified one in the list of table columns. If the IF NOT EXISTS clause is included, the query won’t return an error if the column already exists. ![]() Adds a new column to the table with the specified name, type, codec and default_expr (see the section Default expressions).
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