ALTERDATABASEnewdbSETenable_indexscanTOoff; 使用以下命令可以还原默认配置: ALTERDATABASEnewdbRESETenable_indexscan; 详细的修改选项可以参考官方文档中的ALTER DATABASE语句。 删除数据库 如果不需要,我们可以使用DROP DATABASE语句删除一个数据库: DROPDATABASE[IFEXISTS]name 如果使用了IF EXISTS,删除一个不存在...
DROP TABLE IF EXISTS your_table_name; 如果表存在,则将其删除;如果表不存在,则不执行任何操作。 使用PL/pgSQL函数:可以编写一个PL/pgSQL函数来检查表是否存在,并在需要时抛出自定义错误。 代码语言:sql 复制 CREATE OR REPLACE FUNCTION check_table_exists(table_name text) RETURNS boolean AS $...
postgres=# create database test;CREATEDATABASEpostgres=# alter database testsettablespace mytbs;ALTERDATABASEpostgres=# \c test You are now connected to database"test"asuser"postgres".test=# create tabletb_mytps(i int,namevarchar(32))tablespace mytbs;CREATETABLE 插入实验数据 代码语言:javascript...
postgres@[local]:5432=#\c test pguserYou are now connected to database"test"as user"pguser".test@[local]:5432=#select current_database;ERROR: column"current_database"does not exist LINE 1: select current_database; ^test@[local]:5432=#select current_database();current_database ---test...
Autovacuum uses a visibility map to skip large swaths of the table that haven’t been touched since the last vacuum, and 9.6 took this a step further for anti-wraparound vacuums, but no such optimization exists on the index methods; they are fully scanned every single time. Moreover, t...
CREATE DOMAIN name [AS] data_type [ DEFAULT expression ] [ constraint [ ... ] ]constraint 可以是以下选项之一:[ CONSTRAINT constraint_name ] { NOT NULL | NULL | CHECK (expression) }CREATE FUNCTION定义一个新函数。CREATE [ OR REPLACE ] FUNCTION name ( [ [ arg_name ] arg_type [, .....
SELECT 'CREATE DATABASE <db_name>' WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = '<db_name>')\gexec In this syntax, the NOT EXISTS is used within the WHERE Clause, which will check the existence of a targeted database. If the specified database doesn’t exist, then the...
场景2:误用 if [not] exists 观察上述schema不匹配错误可能会导致"放弃"修复:工程师通常选择盲目地修补代码,而不是找到错误的根本原因.对于上面的示例,可以这样做: createtableifnotexistst1(); 如果此代码不是用于基准测试或测试脚本,而是用于定义一些应用程序的schema,那么这种方法通常是一个坏主意.它用逻辑掩盖了...
help="Database name: Not required for Oracle") parser.add_option ("-l", dest="Authorization_file", type="string", default="", help="Full path and name of authorization file")# Check if value entered for optiontry: (options, args) = parser.parse_args()#Check if ...
1、checkpointer进程本身通过checkpoint_timeout触发 #define CHECKPOINT_CAUSE_TIME 0x0100 /* Elapsed time */ 2、其他进程向checkpointer发送信号触发: #define CHECKPOINT_IS_SHUTDOWN 0x0001 /* Checkpoint is for shutdown */ 主要场景:数据库shutdown时 ...