For more information on the use of statistics by the PostgreSQL query planner, refer to Section 14.2.Ĭhanging per-attribute options acquires a SHARE UPDATE EXCLUSIVE lock. Specify a value of 0 to revert to estimating the number of distinct values normally. This can be useful when the size of the table changes over time, since the multiplication by the number of rows in the table is not performed until query planning time. For example, a value of -1 implies that all values in the column are distinct, while a value of -0.5 implies that each value appears twice on the average. When set to a negative value, which must be greater than or equal to -1, ANALYZE will assume that the number of distinct nonnull values in the column is linear in the size of the table the exact count is to be computed by multiplying the estimated table size by the absolute value of the given number. When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values. 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. 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 Use the pair of the DROP TRIGGER and CREATE TRIGGER statements to replace a trigger by a new one.ALTER TABLE name.Use the ALTER TRIGGER statement to rename a trigger.The following example illustrates how to change the check_salary function of the salary_before_update trigger to validate_salary: BEGIN ĭROP TRIGGER IF EXISTS salary_before_update You can also wrap these statements in a transaction. In order to do so, you can use the DROP TRIGGER and CREATE TRIGGER statements. PostgreSQL doesn’t support the OR REPLACE statement that allows you to modify the trigger definition like the function that will be executed when the trigger is fired. If you use psql tool, you can view all triggers associated with a table using the \dS command: \dS employees The trigger was fired and issued the following error: ERROR: The salary increment cannot that high.ĬONTEXT: PL/pgSQL function check_salary() line 4 at RAISEįinally, use the ALTER TRIGGER statement to rename the before_update_salary trigger to salary_before_update: ALTER TRIGGER before_update_salary Third, create a before update trigger that executes the check_salary() function before updating the salary.įourth, insert a new row into the employees table: INSERT INTO employees(first_name, last_name, salary)įifth, update the salary of the employee id 1: UPDATE employees RAISE 'The salary increment cannot that high.' IF (NEW.salary - OLD.salary) / OLD.salary >= 1 THEN Second, create a function that raises an exception if the new salary is greater than the old one 100%: CREATE OR REPLACE FUNCTION check_salary() Third, specify the new name of the trigger after the RENAME TO keyword.įirst, create new table called employees: DROP TABLE IF EXISTS employees Įmployee_id INT GENERATED ALWAYS AS IDENTITY,.Second, specify the name of the table associated with the trigger after the ON keyword.First, specify the name of the trigger that you want to rename after the ALTER TRIGGER keyword.The following shows the syntax of the ALTER TRIGGER statement: ALTER TRIGGER trigger_name The ALTER TRIGGER statement allows you to rename a trigger. Introduction to PostgreSQL ALTER TRIGGER statement Summary: in this tutorial, you will learn how to use the PostgreSQL ALTER TRIGGER statement to rename a trigger.
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