The following statement inserts some rows into the table: INSERT INTO t3 The following statement creates a new table with a nullable column: CREATE TABLE t3 (c VARCHAR( 50)) Code language: SQL (Structured Query Language) ( sql ) Add a NOT NULL constraint to a nullable column SQL Server issued the following error: String or binary data would be truncated. If the conversion fails, SQL Server terminates the statement and issues an error message.įor example, if you decrease the size of column c to 5 characters: ALTER TABLE t2 ALTER COLUMN c VARCHAR ( 5) Code language: SQL (Structured Query Language) ( sql ) However, when you decrease the size of the column, SQL Server checks the existing data to see if it can convert data based on the new size. You can increase the size of the column as follows: ALTER TABLE t2 ALTER COLUMN c VARCHAR ( 50) Let’s insert some sample data into the t2 table: INSERT INTO t2 The following statement creates a new table with one column whose data type is VARCHAR(10): CREATE TABLE t2 (c VARCHAR( 10)) Code language: SQL (Structured Query Language) ( sql ) Change the size of a column ![]() SQL Server issued the following error: Conversion failed when converting the varchar value to data type int. VALUES ( language: SQL (Structured Query Language) ( sql )įourth, modify the data type of the column from VARCHAR back to INT: ALTER TABLE t1 ALTER COLUMN c INT Third, insert a new row with a character string data: INSERT INTO t1 Second, modify the data type of the column from INT to VARCHAR: ALTER TABLE t1 ALTER COLUMN c VARCHAR ( 2) Second, insert some rows into the table: INSERT INTO t1 The new data type must be compatible with the old one, otherwise, you will get a conversion error in case the column has data and it fails to convert.įirst, create a new table with one column whose data type is INT: CREATE TABLE t1 (c INT) ![]() To modify the data type of a column, you use the following statement: ALTER TABLE table_nameĪLTER COLUMN column_name new_data_type( size) Ĭode language: SQL (Structured Query Language) ( sql ) SQL Server allows you to perform the following changes to an existing column of a table: When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values.Summary: in this tutorial, you will learn how to use the SQL Server ALTER TABLE ALTER COLUMN statement to modify a column of a table. 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
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