在PostgreSQL中,可以使用CASE语句和EXISTS子查询来检查表之间是否存在关系。下面是一个示例: 代码语言:txt 复制 SELECT CASE WHEN EXISTS ( SELECT 1 FROM table1 WHERE table1.column = table2.column ) THEN '存在关系' ELSE '不存在关系' END AS relationship_check FROM table2; 在上面的示例中,我...
[ CONSTRAINT constraint_name ] { UNIQUE ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | PRIMARY KEY ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | CHECK ( expression ) | FOREIGN KEY ( column_name [, ... ] ) REFERENCES ref_table [ ( ref_...
ALTERTABLEpublic.table_nameDROPCOLUMNifexists col3;ALTERTABLEpublic.table_nameDROPCOLUMNcol3 cascade; 九、pg修改字段类型 代码语言:javascript 复制 alter tablepublic.table_name alter column col1 type varcharUSINGcol1::numeric(50,0);alter tablepublic.table_name alter column columnname type oldcolumntyp...
--if-exists 当删除对象时使用IF EXISTS --inserts 以INSERT命令,而不是COPY命令的形式转储数据,使用该选项可以把数据加载到非pg数据库,会使恢复非常慢 该选项为每行生成1个单独的insert命令,?在恢复过程中遇到错误,将会丢失1行而不是全部表数据 --column-inserts 以带有列名的INSERT命令形式转储数据,例如insert ...
COLUMN CONSTRAINT DATATYPE TABLE SCHEMA Supplies the name of a related object. 例子 RAISE EXCEPTION 'Nonexistent ID --> %', user_id USING HINT = 'Please check your user ID'; RAISE 'Duplicate user ID: %', user_id USING ERRCODE = 'unique_violation'; RAISE 'Duplicate user ID: %', ...
例:create table postgtest (id serial primary key,title varchar(255) not null, content text check(length(content) > 3),is_draft boolean default true , create_date timestamp default 'now'); 插入 INSERT INTO TABLE_NAME (column1, column2, column3,...columnN) ...
UNIQUE (column1, ...),唯一约束,括号中的字段值或字段值的组合必须唯一。 PRIMARY KEY(column1, ...),主键约束,定义主键或者复合主键。 REFERENCES,定义外键约束。 CHECK,定义检查约束。 以下示例创建了员工表(employees): CREATETABLEemployees(employee_idINTEGERNOTNULL,first_nameCHARACTERVARYING(20),last_name...
"products_price_min"CHECK(price>0::numeric) 删除字段的默认值相当于将它设置为空值(NULL)。 修改字段数据类型 通常来说,可以将字段的数据类型修改为兼容的类型。 ALTERTABLEtable_nameALTERCOLUMNcolumn_name TYPE new_data_type; 以下语句将产品表的price字段的类型修改为numeric(10,2): ...
* check exists because not all plan node types are robust about being * called again if they've already returned NULL once.) Then call the * executor (we must not skip this, because the destination needs to see a * setup and shutdown even if no tuples are available). Finally, update...
This is arguably more convenient than simply using an ACL on the password column in the underlying table as that would cause a permissions error if queried with SELECT * FROM. When using updateable views, a CHECK OPTION is available when defining the view. When ...