Volatile表很棒,在某种程度上可以与sql server(我的背景)中的临时表相媲美。是否有一种方法来检查是否一个易失性表已经存在?以下代码在第一次运行时无法运行:
DROP TABLE SomeVolatileTable;
CREATE VOLATILE TABLE SomeVolatileTable AS
(
SELECT
TOP 10 *
FROM SomeSourceTable
) WITH DATA ON COMMIT PRESERVE ROWS;
在sql server中,你可以检查一个临时表是否存在:
IF OBJECT_ID('tempdb..#SomeTempTable') IS NOT NULL DROP TABLE #SomeTempTable
Teradata中是否存在类似的东西?
除了返回所有 VT的HELP VOLATILE TABLE
之外,没有办法检查是否存在特定的Volatile Table。
但是您可以像下面这样创建一个存储过程:
/*
Drop a table ignoring 3807 error (Table doesn't exist)
*/
REPLACE PROCEDURE drop_table_if_exists
(
IN db_name VARCHAR(128) CHARACTER SET Unicode,
IN tbl_name VARCHAR(128) CHARACTER SET Unicode,
OUT msg VARCHAR(400) CHARACTER SET Unicode
) SQL SECURITY INVOKER
BEGIN
DECLARE full_name VARCHAR(361) CHARACTER SET Unicode;
DECLARE sql_stmt VARCHAR(500) CHARACTER SET Unicode;
DECLARE exit HANDLER FOR SqlException
BEGIN
IF SqlCode = 3807 THEN SET msg = full_name || ' doesn''t exist.';
ELSE
RESIGNAL;
END IF;
END;
SET full_name = '"' || Coalesce(db_name,DATABASE) || '"."' || tbl_name || '"';
SET sql_stmt = 'DROP TABLE ' || full_name || ';';
EXECUTE IMMEDIATE sql_stmt;
SET msg = full_name || ' dropped.';
END;
它只会忽略Table doesn't exist错误,但仍然会在无效的权限上失败,等等
如果你用自己的用户作为数据库调用它,它也适用于Volatile Tables:
CALL drop_table_if_exists(USER,'SomeVolatileTable', msg);
您可以使用这个存储过程来检查是否存在volatile表:
REPLACE PROCEDURE test_db.VOLATILE_EXISTS(
IN volatile_table_name varchar(30),
OUT exists_ind integer -- 1 if it exists, else 0
)
SQL SECURITY INVOKER
BEGIN
DECLARE ignored_condition varchar(100) default '';
DECLARE table_does_not_exist CONDITION FOR SQLSTATE '42000';
DECLARE sql_string varchar(100);
DECLARE CONTINUE HANDLER FOR table_does_not_exist
SET ignored_condition = 'table does not exist';
SET exists_ind = 0;
SET sql_string = 'select 1 from '||volatile_table_name||' where 1=0';
BEGIN
DECLARE c1 CURSOR FOR s1;
PREPARE s1 FROM sql_string;
OPEN c1;
END;
IF ignored_condition = '' THEN
SET exists_ind = 1;
END IF;
END;
请注意,如果VT不存在,并且您在BEGIN TRANSACTION/END TRANSACTION中调用此SP,"表不存在异常"虽然处理了,但会导致事务回滚作为副作用。
与其在您尝试创建它们之前删除它们,不如在您完成它们之后在脚本中删除它们。这将始终有效,将允许您重新运行而不会出现问题,并将释放volatile表所使用的spool空间。