default_expression:新的默认值表达式。 例如,为 employees 表中的 hire_date 列设置新的默认值: sql ALTER TABLE employees ALTER COLUMN hire_date SET DEFAULT CURRENT_DATE; 修改列的约束: 添加NOT NULL 约束: sql ALTER TABLE table_name ALTER COLUMN column_name SET NOT NULL; 删除NOT NULL 约束: ...
ALTER TABLE table_name DROP COLUMN column_name; 修改表中某列的 DATA TYPE(数据类型),语法如下: ALTER TABLE table_name ALTER COLUMN column_name TYPE datatype; 给表中某列添加 NOT NULL 约束,语法如下: ALTER TABLE table_name MODIFY column_name datatype NOT NULL; 给表中某列 ADD UNIQUE CONSTRAINT...
ALTER TABLE table_name DROP COLUMN column_name; To rename a column, you use the [ALTER TABLE RENAME COLUMN](postgresql-rename-column) TO statement: ALTER TABLE table_name RENAME COLUMN column_name TO new_column_name; To change a default value of the column, you use ALTER TABLE ALTER COLUM...
修改字段.数据结构:ALTER TABLE TABLE_NAME MODIFY COLUMN_NAME DATA_TYPE 字段.名称:ALTER TABLE TABLE_NAME RENAME COLUMN COLUMN_NAME TO NEW_COLUMN_NAME 删除字段:ALTER TABLE TABLE_NAME DROP COLUMN COLUMN_NAME 添加带默认值的列:ALTER TABLE TABLE_NAME ADD COLUMN_NAME DATA_TYPE DEFAULT VAULE 修改列的...
“ALTER COLUMN”commands, along with theTYPEKeyword, are used to change/modify the data type of a column. For example, integer to character, text to varchar, and so on. InPostgreSQL, we can change the data type of one or more than one column using the“ALTER TABLE”and“ALTER COLUMN”...
于是想到通过default来修改列的默认值: alter table A modify column biz default 'old' comment '业务标识 old-老业务, new-新业务'...找后台运维查生产数据库,发现历史数据的biz字段还是null 原因:自己在本地mysql数据库试了下,好像的确是default没法修改历史数据为null 的值。这就尴尬了。...看起来mysql和...
1--表字段备注2COMMENTONcolumnsuggest.idis'主键'; 16.把int4类的主键改成int8 ALTERTABLE"public"."tableName"ALTERCOLUMN"id" TYPE int8 USING "id"::int8; 17.建表时,主键int8自增 "id" bigserialPRIMARYKEY 18.创建默认时间 "modify_time"timestamp(6)defaultnow()...
ALTER TABLE public.table_name ADD COLUMN col3 string DEFAULT ''; 六、pg删除字段默认值 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ALTER TABLE public.table_name ALTER COLUMN col3 DROP DEFAULT; 七、pg新增字段 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ALTER TABLE public.table_na...
CREATE INDEX c_idx2 ON locktest(c);ALTER TABLE locktest ADD COLUMN c2 INT;CREATE INDEX c2_idx ON locktest(c2);-- unfinished example transaction BEGIN;UPDATE locktest SETc=3WHEREc=1;-- second connectionpostgres=# SELECT * FROM lockview;pid|vxid|lock_type|lock_mode|granted|xid_lock|rel...
When a table becomes very large, the number of dead rows allowed per the default autovacuum settings also grows. For a table with just one billion rows, cleanup won’t begin until 200,000,000 rows have been updated or deleted. In most workloads, that takes a while to achieve. When i...