Let’s see a similar example in which we will cast the ‘fullname’ column from the char type to varchar. For example, the conversion from char to varchar is done implicitly. When you try to change the column type, PostgreSQL checks if the type cast can be done implicitly.

Note that, if any of the values in the column doesn’t have a length greater than the newly mentioned size, you won’t get any error. In this case, you must update the values first from the table and then try the ALTER query again. Note that, if you decrease the size limit of the column but the column already consists of values that have a length greater than the newly mentioned size (the reduced size), you will get an error as PostgreSQL doesn’t allow you to do so. Let’s see the table description and check if the size limit of the column is increased.

Here, we have set the same data type to the ‘fullname’ column, however, we have specified more length. SET DATA TYPE CHAR( 30) Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) So, let’s increase the column size using the syntax we learned earlier. However, some names might exceed this length. In the above table, the ‘fullname’ column has a length of 20 characters. For the further demonstration purpose, we kept it as a VARCHAR. Note that, although the ‘prn_number’ is a VARCHAR column, it consists of the numeric values. Here, we created a ‘student’ table having four different data types.

INSERT INTO student (age, fullname, prn_number)Ĭode language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) Student Table Description Student Table Data PostgreSQL Modify Column Type Examplesīefore proceeding, we will need a table having columns of a variety of data types. Let’s see some examples now so that you will understand its real-time usage. To modify the multiple columns’ data type, write multiple ALTER COLUMN statements separated by a comma. If the existing data type is not convertible to the new data type, you will get an error message. The ‘type’ keyword must be specified in order to set the new data type. SET DATA TYPE – Here, SET DATA is an optional keyword.columnName – The name of the column that you want to change the data type of.If not, it will not throw the error message. IF EXISTS – It checks if the table name that you mentioned exists.When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values.ALTER COLUMN columnName type newDataType Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) n_distinct affects the statistics for the table itself, while n_distinct_inherited affects the statistics gathered for the table plus its inheritance children. Currently, the only defined per-attribute options are n_distinct and n_distinct_inherited, which override the number-of-distinct-values estimates made by subsequent ANALYZE operations. This form sets or resets per-attribute options. SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. For more information on the use of statistics by the PostgreSQL query planner, refer to Section 14.2. The target can be set in the range 0 to 10000 alternatively, set it to -1 to revert to using the system default statistics target ( default_statistics_target). This form sets the per-column statistics-gathering target for subsequent ANALYZE operations. sequence_option is an option supported by ALTER SEQUENCE such as INCREMENT BY. These forms alter the sequence that underlies an existing identity column. If DROP IDENTITY IF EXISTS is specified and the column is not an identity column, no error is thrown. Like SET DEFAULT, these forms only affect the behavior of subsequent INSERT and UPDATE commands they do not cause rows already in the table to change. These forms change whether a column is an identity column or change the generation attribute of an existing identity column.

RENAME CONSTRAINT constraint_name TO new_constraint_nameĪLTER TABLE ALL IN TABLESPACE name ]ĪTTACH PARTITION partition_name AS IDENTITY

Postgresql modify column type