Introduction to the PostgreSQL ADD COLUMN statement To add a new column to an existing table, you use the ALTER TABLE ADD COLUMN statement as follows: ALTER TABLE table_name ADD COLUMN new_column_name data_type constraint; In this syntax: First, specify the name of the table to which you...
ADD [ COLUMN ] column_type [ column_constraint [ ... ] ] DROP [ COLUMN ] column [ RESTRICT | CASCADE ] ALTER [ COLUMN ] column TYPE type [ USING expression ] ALTER [ COLUMN ] column SET DEFAULT expression ALTER [ COLUMN ] column DROP DEFAULT ALTER [ COLUMN ] column { SET | DROP...
alter table [表名] add column [字段名] [类型]; *删除表中的字段: alter table [表名] drop column [字段名]; *重命名一个字段: alter table [表名] rename column [字段名A] to [字段名B]; *给一个字段设置缺省值: alter table [表名] alter column [字段名] set default [新的默认值]; ...
postgres=# \help SELECT Command: SELECT Description: retrieve rows from a table or view Syntax: [ WITH [ RECURSIVE ] with_query [, ...] ] SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ] [ * | expression [ [ AS ] output_name ] [, ...] ] [ FROM from_item [,...
A new column backend_type identifies the process type. Prevent unnecessary checkpoints and WAL archiving on otherwise-idle systems (Michael Paquier) Increase the maximum configurable WAL segment size to one gigabyte (Beena Emerson) Add columns to pg_stat_replication to report replication delay ...
Use the same syntax as above, use the ALTER COLUMN statement and the TYPE keyword followed by the new data type:Example Change the color column from VARCHAR(255) to VARCHAR(30): ALTER TABLE cars ALTER COLUMN color TYPE VARCHAR(30); Result ALTER TABLE...
PostgreSQL is free and open-source. Start learning PostgreSQL now ❯ Learning by Doing In this tutorial you get a step by step guide on how to install and create a PostgreSQL database. You will learn how to create a project where you can create, read, update, and delete data. ...
-- Alternative syntax for string literal: CREATE FUNCTION one() RETURNS integer AS ' SELECT 1 AS result; ' LANGUAGE SQL; SELECT one(); -- 返回空 CREATE FUNCTION clean_emp() RETURNS void AS ' DELETE FROM emp WHERE salary < 0;
SELECT json_agg(my_column) FROM my_table; This will produce a JSON array that encompasses the values found in the “my_column” column of the “my_table” table. 5. jsonb_set function This function modifies a JSON object field by assigning it a new value. For example, ...
Syntax:CREATEEVENTTRIGGER nameONevent[ WHEN filter_variableIN(filter_value [, ... ]) [AND... ] ] EXECUTEPROCEDUREfunction_name() 1、事件触发器的触发点(event) 目前支持4个触发点(event) ddl_command_start, ddl_command_end, table_rewrite and sql_drop ...