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 [,...
postgres=#\helpcreatetablespace;Command:CREATETABLESPACEDescription:defineanewtablespaceSyntax:CREATETABLESPACEtablespace_name[OWNER{new_owner|CURRENT_ROLE|CURRENT_USER|SESSION_USER}]LOCATION'directory'[WITH(tablespace_option=value[,...])]--创建表空间abc_tbs,实现准备对应的目录[postgres@centos79~]$ls-lrt...
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...
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 ...
Syntax: CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name ( [ { column_name data_type [ STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT } ] [ COMPRESSION compression_method ] [ COLLATE collation ] [ column_constraint [ .....
PL/pgSQL is a procedural language similar to Oracle's PL/SQL. It's much more powerful than pure SQL in that it supports variables, conditional expressions, looping constructs, exceptions, and the like. Because it natively supports all of PostgreSQL's SQL syntax, you can consider it a supers...
PostgreSQL使用角色的概念管理数据库访问权限。根据角色的设置方式,可以将角色视为数据库用户或数据库用户组。角色可以拥有数据库对象(例如,表和函数),并可以将对这些对象的权限分配给其他角色,以控制谁有权访问哪些对象。此外,还可以将角色的成员资格授予另一个角色,从而允许成员角色使用分配给另一个角色的权限。