sql ALTER TABLE employees DROP COLUMN middle_name; 验证列是否已成功从表中删除: 你可以通过查询表的结构来验证列是否已被成功删除。这可以通过DESC命令或查询ALL_TAB_COLUMNS视图来实现。 sql DESC employees; 或者: sql SELECT COLUMN_NAME FROM ALL_TAB_COLUMNS WHERE TABLE_NAME = 'EMPLOYEES' AND OWNER...
Oracle Drop Column using DROP COLUMN clause To drop a column from a table physically, you use the following statement: ALTERTABLEtable_nameDROPCOLUMNcolumn_name;Code language:SQL (Structured Query Language)(sql) To drop multiple columns, you use the statement below: ...
我 们要删除表中不用的字段,如果直接drop column,对于大表,进行DDL操作的时间会比较长,会严重阻塞DML语句,导致应用服务器crash,通常的做法是先set unused column column_name 或者 set unused column_name,column_name...,然后再利用停机时间做alter table table_name drop unused columns。 做如下实验: SQL> sel...
Oracle Database/ Release 23 SQL Language Reference Purpose Use theDROPTABLEstatement to move a table or object table to the recycle bin or to remove the table and all its data from the database entirely. Note: Unless you specify thePURGEclause, theDROPTABLEstatement does not result in space...
SQL> ALTER TABLE t1 DROP UNUSED COLUMNS; ALTER TABLE t1 DROP UNUSED COLUMNS * ERROR at line 1: ORA-39726: unsupported add/drop column operation on compressed tables SQL> alter table t1 compress for oltp; Table altered. SQL> ALTER TABLE t1 DROP UNUSED COLUMNS; ...
SQL> alter table test_compress compress for all operations; Table altered. SQL> alter table test_compress drop column object_name; Table altered. In 11g it is allowed to drop columns from a compressed table IF compatible is set to 11.1 or higher AND table was created with the "compress for...
SQL> alter table test_compress compress for all operations; Table altered. SQL> alter table test_compress drop column object_name; Table altered. In 11g it is allowed to drop columns from a compressed table IF compatible is set to 11.1 or higher AND table was created with the "compress for...
Now, if a new column is to be added or an old column is to be dropped from a table, the contents of existing rows should be changed to reflect the correct values of columns present in the table. And, as the number of rows in the table increases, time taken to modify all existing ...
创建drop columns查询是指在数据库中删除一个或多个列。下面是一个完善且全面的答案: 在关系型数据库中,可以使用ALTER TABLE语句来创建drop columns查询。具体步骤如下: 首先,使用ALTER TABLE语句指定要修改的表名。 然后,使用DROP COLUMN子句指定要删除的列名。 最后,执行该ALTER TABLE语句以应用更改。 下面是一个...
20)PARENT_ID NUMBERDEPTH NUMBERPOSITION NUMBERSEARCH_COLUMNS NUMBERCOST NUMBERCARDINALITY NUMBERBYTES NUMBEROTHER_TAG VARCHAR2(35)PARTITION_START VARCHAR2(64)PARTITION_STOP VARCHAR2(64)PARTITION_ID NUMBEROTHER VARCHAR2(4000)DISTRIBUTION VARCHAR2(20)CPU_COST NUMBERIO_COST NUMBERTEMP_...