postgresql中,许多ddl语句支持if exists、if not exists。例如: postgres=# create table if not exists abce(); CREATE TABLE postgres=# drop table if exists abce; DROP
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...
CREATE TABLE IF NOT EXISTS skills( Id serial, Userid integer NOT NULL, Name VARCHAR(10) NOT NULL, CreatedAt timestamptz DEFAULT current_timestamp, UpdatedAt timestamptz DEFAULT current_timestamp, CONSTRAINT skills_pkey PRIMARY KEY(Id), CONSTRAINT skills_Userid_fkey FOREIGN KEY(Userid) ...
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...
*/ bool typisdefined; char typdelim; /* delimiter for arrays of this type */ Oid typrelid; /* 0 if not a composite type */ Oid typelem; Oid typarray; regproc typinput; /* text format (required) */ regproc typoutput; regproc typreceive; /* binary format (optional) */ regproc...
No pg_config...trying anyway.If building fails,pleasetryagainwith--with-pg-config=/path/to/pg_config checkingforlibpq-fe.h...no Can't find the 'libpq-fe.h header***extconf.rb failed***Could not create Makefile due to some reason,probably lackofnecessary ...
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 ...
Is Null –check if a value is null or not. Section 3. Joining Multiple Tables Joins –show you a brief overview of joins in PostgreSQL. Table aliases –describes how to use table aliases in the query. Inner Join–select rows from one table that have the corresponding rows in other tables...
-- Lock not acquired END IF; -- Transaction 1 COMMIT; 更多关于大数据 PostgreSQL 系列的学习文章,请参阅:PostgreSQL 数据库,本系列持续更新中。 监控锁 所有活动事务持有的监控锁的基本配置即为系统视图 pg_locks[4]。这个视图为每个可加锁的对象、已请求的锁模式和相关事务包含一行记录。非常重要的一点是,pg...
布尔变量只有TRUE、FALSE和NULL三个值,可以通过逻辑操作符AND、OR和NOT对变量进行比较并返回一个布尔值。 例程: DECLARE tside BOOLEAN := TRUE; fside BOOLEAN := FALSE; eside BOOLEAN := NULL; BEGIN eside := tside OR fside; IF eside THEN ...