解答1: 如果表中已经存在相同名称的字段,可以使用ALTER TABLE语句的RENAME子句先重命名现有字段,然后再添加新字段。 ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name; ALTER TABLE table_name ADD (new_column_name datatype [DEFAULT default_value]); old_column_name是要重命名的现有...
tables without LOBcolumns), if you specify both a NOT NULL constraint and adefault value, the database can optimize the column add operation and greatlyreduce the amount of time that the table is locked for DML.
alter table nop_auth_dept add NOP_TENANT_ID VARCHAR(32) DEFAULT '0' NOT NULL; alter table nop_auth_ext_login add column NOP_TENANT_ID VARCHAR(32) DEFAULT '0' NOT NULL; alter table nop_auth_ext_login add NOP_TENANT_ID VARCHAR(32) DEFAULT '0' NOT NULL; alter table nop_auth_group...
The followingstatement alters thehr.admin_emptable to add a new columnnamedbonus: ALTER TABLE hr.admin_emp ADD (bonus NUMBER (7,2)); If a new columnis added to a table, the column is initiallyNULLunless you specifytheDEFAULTclause. When you specify a default value, the databaseimmediately...
添加字段的语法:alter table tablename add (column datatype [default value][null/not null],….); 修改字段的语法:alter table tablename modify (column datatype [default value][null/not null],….); 删除字段的语法:alter table tablename drop (column); ...
在Oracle中,在高并发、高负载的情况下,如何给表添加字段并设置DEFAULT值? ♣ 答案部分 在Oracle 12c之前,当Oracle表数据量上亿时,对表执行“ALTER TABLE XXX ADD COLUMN_XX VARCHAR2(2) DEFAULT 'XXX';”操作时,效率及安全性是必须要考虑的因素。若直接执行,则会在该过程中给表加上6级表锁,也就是连查询...
添加字段的语法:alter table tablename add (column datatype [default value][null/not null],….); 修改字段的类型的语法:alter table tablename modify (column datatype [default value][null/not null],….); 删除字段的语法: ALTER TABLE table_name(MODIFY column_name column_type , ... ); 例子...
在Oracle 12c之前,当Oracle表数据量上亿时,对表执行“ALTER TABLE XXX ADD COLUMN_XX VARCHAR2(2) DEFAULT 'XXX';”操作时,效率及安全性是必须要考虑的因素。若直接执行,则会在该过程中给表加上6级表锁,也就是连查询都需要等待,这在生产库上是相当危险的操作。因为Oracle在执行上述操作过程中,不仅要更新数据...
public class DefaultColumnValue extends java.lang.Object implements ColumnValueThe DefaultColumnValue class provides an Oracle default implementation of ColumnValue interface.See Also: RowLCRField Summary Fields inherited from interface oracle.streams.ColumnValue BFILE, BINARY_DOUBLE, BINARY_FLOAT, BOOLEAN,...
(TO_CHAR(first_time, 'HH24'), '23', 1, 0)) H23, COUNT(*) TOTAL FROM (SELECT ROWNUM RN, FIRST_TIME FROM V$LOG_HISTORY WHERE first_time>sysdate-18 and FIRST_TIME>ADD_MONTHS(SYSDATE,-1) ORDER BY FIRST_TIME) GROUP BY TO_CHAR(first_time, 'MM/DD') ORDER BY MIN(RN); #查询...