在PostgreSQL中,使用ALTER TABLE语句修改列的数据类型需要用到ALTER COLUMN子句。具体的语法是: sql ALTER TABLE table_name ALTER COLUMN column_name TYPE new_data_type USING old_data_type::new_data_type; 其中,table_name是要修改的表名,column_name是要修改的列名,new_data_type是新的数据类型,old_data...
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....
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>ALTER COLUMN<column_name>TYPE<new_data_type>USING<expression>; The following changes the data type of thesalarycolumn fromintegertoINT. Example: Modify Column Datatype Copy ALTER TABLE employee ALTER COLUMN salary TYPE integerUSINGsalary::INT; Alter Column Type using pgAdmin...
alter table test_tb rename column test_msg to 2.4、修改表名: Rename 表名1 (旧名字)to 表名2(新名字) rename test_tb to 2.5、修改表字段 表名modify( 字段名称 新的字段类型 ) alter table test_tb1 modify(msg varchar(4000)) 2.6、添加表约束: ...
CREATEINDEX index_nameONtable_name (column_name, ...);2) 并发创建索引(在线创建索引)。CREATEINDEX CONCURRENTLY3)删除索引DROPINDEX idx_name;dropindex concurrently idx_name;4)查看表的所有索引信息select*frompg_indexeswheretablename='student';5)显示关于访问特定索引的I/O统计信息。select*frompg_statio...
column?---(null) (1 row) This shows that in the presence of nulls, the IN predicate will only return true or null – never false. It follows that NOT IN will only return false or null – never true! When giving a list of constants like that, it is easy to spot when there ar...
“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”...
限制:除了ADD COLUMN外,无法识别用户的其他DDL操作。 不支持ALTER TABLE/CREATE TABLE。 不支持TEMPORARY表、UNLOGGED表和Hyper表复制,PostgreSQL数据库没有提供机制来对这两种类型的表进行log解析订阅。 不支持Sequences复制(serial/bigserial/identity)。 不支持TRUNCATE操作。
columnN datatype,PRIMARYKEY( oneormore columns ) ); 删除表: droptablestudent2; 创建模式(架构): 模式(也叫架构)是指定的表集合。 它还可以包含视图,索引,序列,数据类型,运算符和函数。 CREATESCHEMAschema_name; 插入数据: INSERTINTOTABLE_NAME (column1, column2, column3,...columnN)VALUES(value1,...