启用约束并检查现有数据是否符合约束,由于表中存在不符合约束条件的数据,故产生报错。 ALTERTABLEaaENABLECONSTRAINTaa_a1_check; ERROR:checkconstraint"aa_a1_check"isviolatedbysomerow 启用约束不检查现有数据是否符合约束。 ALTERTABLEaaENABLECONSTRAINTaa_a1_checkNOTVALID;ALTERTABLE 插入不符合约束条件的数据,产生报错。
ALTER TABLE employees ENABLE CONSTRAINT emp_emp_id_pk CASCADE;语句中指定CASCADE关键字，这样将在禁用主分键约束的同时禁用那些引用它们的FOREIGN KEY约束，在禁用后，该表可能会插入重复健，一般情况下是不允许这样操作的，三思而行！
reference_definition|ADD[CONSTRAINT[symbol]]CHECK(expr) [[NOT] ENFORCED]|DROP{CHECK|CONSTRAINT} symbol|ALTER{CHECK|CONSTRAINT} symbol [NOT] ENFORCED|ALTERINDEX index_name {VISIBLE|INVISIBLE}|{DISABLE|ENABLE} KEYS|DROP{INDEX|KEY} index_name|DROPPRIMARYKEY|DROPFOREIGNKEY fk_symbol|RENAME {INDEX|KEY}...
ALTER TABLE modifies a table definition by altering, adding, or dropping columns and constraints. ALTER TABLE also reassigns and rebuilds partitions, or disables and enables constraints and triggers.
alter table emp add constraint qwe unique(ename) ——— 4.默认约束: 意思很简单就是让此列的数据默认为一定的数据 格式: alter table 表名称 add constraint 约束名称 约束类型 默认值) for 列名 比方说:emp表中的gongzi列默认为10000 alter table emp add constraint...
check_constraint_definition:[CONSTRAINT [symbol]]CHECK(expr)[[NOT]ENFORCED] table_options: table_option[[,]table_option] ... table_option: AUTO_INCREMENT[=]value|AVG_ROW_LENGTH[=]value|[DEFAULT]CHARACTERSET[=]charset_name|CHECKSUM[=]{0|1}|[DEFAULT]COLLATE[=]collation_name|COMMENT[=]'string...
ALTER TABLE Customer ADD CONSTRAINT Con_First UNIQUE (Address); Oracle: ALTER TABLE Customer ADD CONSTRAINT Con_First UNIQUE (Address); SQL Server: ALTER TABLE Customer ADD CONSTRAINT Con_First UNIQUE (Address); Con_First是限制的名称。
alter table 表名 add constraint 约束名称 约束类型(列名) 比方说可以给ename列加个unique,让ename列的数据不重复 例子: alter table emp add constraint qwe unique(ename) ——— 4.默认约束: 意思很简单就是让此列的数据默认为一定的数据 格式: alter...
constraint_clauses::= alter_table_partitioning::= alter_external_table_clauses::= move_table_clause::= enable_disable_clause::= After each clause you will find links to its component subclauses. alter_table_properties::= Description of the illustration alter_table_properties.gif ...
To force use of the COPY algorithm for an ALTER TABLE operation that would otherwise not use it, specify ALGORITHM=COPY or enable the old_alter_table system variable. If there is a conflict between the old_alter_table setting and an ALGORITHM clause with a value other than DEFAULT, the ALG...