DROPTABLEIFEXISTSyour_table_name; 如果表存在,则将其删除;如果表不存在,则不执行任何操作。 使用PL/pgSQL函数:可以编写一个PL/pgSQL函数来检查表是否存在,并在需要时抛出自定义错误。 代码语言:sql 复制 CREATEORREPLACEFUNCTIONcheck_table_exists(table_nametext)RETURNSboolea
You have a table address and want to check if there’s already a row with address_id = 100 existing. You can use COUNT to check: SELECT COUNT(*) FROM address WHERE address_id = 100; But if you are looking for a faster query with a yes/no answer: SELECT EXISTS(SELECT 1 FROM ...
>>> create table if not exists people(name text,age int(2),gender char(1)); 如上代码表示...
table_constraint 可以是以下选项之一:[ CONSTRAINT constraint_name ] { UNIQUE ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | PRIMARY KEY ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | CHECK ( expression ) | FOREIGN KEY ( column_name [, ... ] ...
DROPTABLE[IF EXISTS]name[CASCADE | RESTRICT]; 其中,name表示要删除的表;如果使用了IF EXISTS,删除一个不存在的表不会产生错误,而是显示一个信息。以下语句将会删除表emp1: DROPTABLEemp1; 如果被删除的表存在依赖于它的视图或外键约束,需要指定CASCADE选项执行级联删除。
The EXISTS operator is used to test for the existence of any record in a sub query.The EXISTS operator returns TRUE if the sub query returns one or more records.Example Return all customers that is represented in the orders table: SELECT customers.customer_name FROM customers WHERE EXISTS ( ...
CREATETABLE IF NOT EXISTS tab_name(first_coldata_type,second_coldata_type,third_coldata_type,...nth_coldata_type); Here, the IF NOT EXISTS clause will first check the existence of the targeted table. If the table already exists, then a notice will be issued instead of throwing an error...
--exclude-table-data=PATTERN do NOT dump data for the specified table(s) --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...
the CREATE TABLE IF NOT EXISTS command will simply not create a new table, and PostgreSQL will not throw an error. However, it’s important to note that it will not check for the structure of an existing table—if a table with the same name but different columns exists, it won’t atte...
可以看到所有节点都保存了一份相同的数据。 使用IF NOT EXISTS 带IF NOT EXISTS 关键字作用表示表不存在时才创建。 postgres=# create table t(id int,mc text); CREATE TABLE postgres=# create table t(id int,mc text); ERROR: relation"t"already exists postgres=...