ALTER [ COLUMN ] column TYPE type [ USING expression ] ALTER [ COLUMN ] column SET DEFAULT expression ALTER [ COLUMN ] column DROP DEFAULT ALTER [ COLUMN ] column { SET | DROP } NOT NULL ALTER [ COLUMN ] column SET STATISTICS integer ALTER [ COLUMN ] column SET STORAGE { PLAIN | EXT...
ALTER TABLE students ALTER COLUMN age TYPE integer; 注意:修改字段类型可能会影响表中已有的数据,如果新旧数据类型不兼容,该操作将失败。 3、修改字段默认值 修改字段默认值可以使用以下命令: ALTER TABLE 表名 ALTER COLUMN 字段名 SET DEFAULT 新默认值; 示例: ALTER TABLE students ALTER COLUMN age SET DEFAU...
alter table [表名] alter column [字段名] set default [新的默认值] 给一个字段设置缺省值 alter table [表名] alter column [字段名] drop default 去除缺省值 insert into 表名 ([字段名m],[字段名n],...) values ([列m的值],[列n的值],...) 在表中插入数据 update [表名] set [目标字...
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]; *去除缺省值: alter table [表名] alter column [字段名] drop default;...
-- 创建一个示例表 CREATE TABLE users ( id SERIAL PRIMARY KEY, name VARCHAR(50) ); -- 更改字段序列 ALTER TABLE users ALTER COLUMN id SET DEFAULT nextval('users_id_seq'); ALTER TABLE users ALTER COLUMN id SET NOT NULL; SELECT setval('users_id_seq', (SELECT MAX(id) FROM users)); ...
ALTERTABLEtable_nameALTERCOLUMNcolumn_nameSETDEFAULTvalue; 我们将为产品表的价格设置一个默认值 test=#ALTERTABLEproductsALTERCOLUMNpriceSETDEFAULT8.88;ALTERTABLEtest=# \d products;Table"hr.products"Column|Type|Collation|Nullable|Default---+---+---+---+---product_no|integer||notnull|name|text|||pr...
ALTER TABLE tablename ALTER COLUMN id SET DEFAULT null; DROP SEQUENCE IF EXISTS sequence_name; -- 设置起始值,id_max 即 id 目前的最大值,可写为1,可通过 “SELECT MAX(id) FROM tablename” 得到 CREATE SEQUENCE sequence_name START WITH id_max; ...
Postgres allows us to set the TIMESTAMP as the default value of an already existing table’s column: ALTERTABLEtbl_nameALTERCOLUMNcol_nameSETDEFAULTdefault_val; Example 1: Setting a Column’s Default Value While Table Creation Let’s create a new sample table named “std_details” with t...
ADD COLUMN "col_name" BOOLEAN DEFAULT FALSE; This way might take longer if the operation is huge. You should also update the nullability of the new column: ALTER TABLE table_name ALTER COLUMN col_name SET NOT NULL; Need a good GUI Tool for PostgreSQL? TablePlus is a modern, native tool...
To change the data type, or the size of a table column we have to use the ALTER TABLE statement.The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.The ALTER TABLE statement is also used to add and drop various constraints on an existing table....