如果新字段需要设置默认值,可以使用DEFAULT关键字: ALTER TABLE your_table_name ADD COLUMN new_column_name column_data_type DEFAULT default_value; 在这里,将default_value替换为你希望设为默认值的具体值。 如果新字段不允许NULL值,可以使用NOT NULL约束: ALTER TABLE your_table_name ADD COLUMN new_column_...
ALTERTABLE xADDCOLUMN z textDEFAULT'some value'; then it took long time. How long it did depend on size of table. This was because postgresql was actually rewriting the whole table, adding the column to each row, and filling it with default value....
1. it was virtually instantaneous. Get a lock on table, add information about new column to system catalogs, and it's done. But when you tried: ALTER TABLE x ADD COLUMN z text DEFAULT 'some value'; 1. then it took long time. How long it did depend on size of table. This was be...
2、新增字段,并添加默认值,由于只需要修改元数据,瞬间完成。 postgres=#altertableaaaaddcolumnc1textdefault'digoal';ALTERTABLETime:3.013ms 3、查看元数据表,可以看到,atthasmissing=true, attmissingval=我们设置的默认值。 postgres=# \xExpanded display is on. postgres=# select * from pg_attribute where ...
Then set a default value for the new column in a separate statement: ALTER TABLE table_name ALTER COLUMN col_name SET DEFAULT FALSE; Or you can put them all together in a single statement: ALTER TABLE table_name ADD COLUMN "col_name" BOOLEAN DEFAULT FALSE; ...
ALTERTABLEtable_nameALTERCOLUMNcolumn_name TYPE new_data_type USING expression; 我们先为产品表增加一个字符串类型的字段level,然后将其修改为整数类型。 test=#ALTERTABLEproductsADDCOLUMNlevelVARCHAR(10);ALTERTABLEtest=#ALTERTABLEproductsALTERCOLUMNlevelTYPEINTEGER; ...
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 allows us to set a TIMESTAMP as the column’s default value. For this purpose, the DEFAULT keyword is used with the column name at the time of table cr…
在已有表里添加/删除字段:alter table 表名 add/drop column 字段名 类型/字段名 6.psql 导入、导出表数据:\copy (1)导入数据:COPY 表名 from '数据文本的绝对路径';(注:COPY 命令只有超级用户才能使用) 也可用\copy 表名 from '数据文本的绝对路径';(没有超级用户权限的情况下,需要导出小表数据,通常使用...
ALTER TABLE(包括RENAME TABLE、ADD COLUMN、ADD COLUMN DEFAULT、ALTER COLUMN TYPE、DROP COLUMN、ADD CONSTRAINT、ADD CONSTRAINT CHECK、ALTER COLUMN DROP DEFAULT) TRUNCATE TABLE(源库PostgreSQL为PostgreSQL 11及以上版本) CREATE INDEX ON TABLE 重要 不支持迁移DDL中包含的附加信息,如CASCADE或RESTRICT等。 不支...