digoal=# select null not between 1 and null; ?column? --- UnKnown (1 row) 1. 2. 3. 4. 5. 2. case, 注意CASE中如果使用NULL, 是使用的=操作符. 所以null分支用于不会执行. 如下 : digoal=# select case 1 when null then 'is null' else 'is not null' end; case --- is not null...
还有!~~和!~~*操作符分别代表NOT LIKE和NOT ILIKE。所有这些操作符都是PostgreSQL特有的。 2. SIMILAR TO正则表达式: SIMILAR TO根据模式是否匹配给定的字符串而返回真或者假。 string SIMILAR TO pattern [ESCAPE escape-character] string NOT SIMILAR TO pattern [ESCAPE escape-character] 它和LIKE非常类似,...
postgres=#createtableifnotexists abce(); CREATETABLE postgres=#droptableif exists abce; DROPTABLE postgres=# 建议只是在必须的时候在ddl中使用if exists、if not exists。以下是三个示例,展示了过度使用他们而产生的负面效应。 示例1:create table if not exists 假设我们使用以下一些工具(如Flyway、Sqitch或嵌...
typedefstructMemoryContextData{NodeTag type;/*内存节点类型 identifies exact kind of context */MemoryContextMethods*methods;/*内存处理函数指针 virtual function table */MemoryContext parent;/*父节点指针 NULL if no parent (toplevel context) */MemoryContext firstchild;/*第一个子节点 head of linked li...
/* If not NULL, Executor is active; call ExecutorEnd eventually: */ //如不为NULL,执行器处于活动状态 QueryDesc *queryDesc; /* 执行器需要使用的信息;info needed for executor invocation */ /* If portal returns tuples, this is their tupdesc: */ ...
IS NOT NULL PostgreSQL 针对不同的类型,需要创建不同的函数 和 <=>createor replacefunctionnulleq(int,int)returnsintas$$declarebeginif$1isnulland$2isnullthenreturn1;elsereturn0;endif;end; $$languageplpgsql; postgres=#createoperator<=> (procedure=nulleq,leftarg=int,rightarg=int);CREATEOPERATORpostgr...
) except (Exception, DatabaseError) as e: print("操作失败:", e) finally: # 释放数据库连接 if connection is not None: connection.close() print("PostgreSQL 数据库连接已关闭。") 同样是先连接数据库;然后利用游标对象的 execute() 方法执行 SQL 命令创建表;commit 方法用于提交事务修改,如果不执行...
drop indexifexists"t_user_pkey";alter table"t_user"add constraint"t_user_pkey"primarykey("ID"); 根据已有表结构创建表 代码语言:javascript 复制 create tableifnot exists新表(like 旧表 including indexes including comments including defaults); ...
CREATETABLEIFNOTEXISTSpublic.disaccount(id serialNOTNULL,store_id smallintNOTNULL,first_name charactervarying(45)COLLATEpg_catalog."default"NOTNULL,last_name charactervarying(45)COLLATEpg_catalog."default"NOTNULL,sell_number smallintNOTNULL,sell_discount float,sell_update timestamp without time zoneDEF...
POSTGRESQL没有IFNULL函数，有 COALESCE COALESCE(value [, ...])The COALESCE function returns the first of its arguments that is not null. Null is returned only if all arguments are null. It is often used to substitute a default value for null values when data is retrieved for ...