alter table student add constraints fk_student_cid foreign key(cid) references clazz(cno) on delete set null alter table student drop constraints fk_student_cid drop table student --添加测试数据 insert into student values(1,'张三001',18,'男','唱歌','657889900',1); insert into student value...
[ CONSTRAINT constraint_name ] { NOT NULL | NULL | UNIQUE [ USING INDEX TABLESPACE tablespace ] | PRIMARY KEY [ USING INDEX TABLESPACE tablespace ] | CHECK (expression) | REFERENCES ref_table [ ( ref_column ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE action ] [ ...
权限类型包括:SELECT、INSERT、UPDATE、DELETE、TRUNCATE、REFERENCES、TRIGGER、CREATE、CONNECT、TEMPORARY、EXECUTE、USAGE、SET、ALTER SYSTEM。 详情如下: SELECT 允许从表、视图、具体化视图或其他类似表的对象的任何列或特定列执行 SELECT 操作。 还允许使用 COPY TO。 UPDATE、DELETE 或 MERGE 也需要此权限。 对于SE...
16394 | lib1 | 15288 | postgres | idle | 127.0.0.1 | SET application_name = 'PostgreSQL JDBC Driver' 16394 | lib1 | 12872 | postgres | idle | 127.0.0.1 | SET application_name = 'PostgreSQL JDBC Driver' 16394 | lib1 | 13108 | postgres | idle | 127.0.0.1 | SET application_name ...
WHEN'n'THEN'SET NULL' WHEN'd'THEN'SET DEFAULT' ENDASon_update, CASEconfdeltype WHEN'a'THEN'NO ACTION' WHEN'r'THEN'RESTRICT' WHEN'c'THEN'CASCADE' WHEN'n'THEN'SET NULL' WHEN'd'THEN'SET DEFAULT' ENDASon_delete, CASEconfmatchtype ...
ON TABLES TO { [ GROUP ] role_name | PUBLIC } [, ...] [ WITH GRANT OPTION ] ... ALTER DOMAIN 修改一个域的定义。 ALTER DOMAIN name { SET DEFAULT expression | DROP DEFAULT } ALTER DOMAIN name { SET | DROP } NOT NULL ALTER DOMAIN name ADD domain_constraint ...
UPDATEtable_nameSETcolumn1=value1,column2=value2...,columnN=valueNWHERE[condition];UPDATEemploySETage=23,salary=11000WHEREid=1; 4.删除数据(DELETE语句)DELETE语句用于从表中删除现有记录。 “WHERE”子句用于指定删除所选记录的条件,如是不指定条件则将删除所有记录。 语法...
如果在分区设计中考虑了使用模式,则可以通过添加或删除分区来完成批量加载和删除。使用 DROP TABLE 或执行 ALTER TABLE DETACH PARTITION 删除单个分区比批量操作快得多。这些命令还完全避免了由批量 DELETE 引起的 VACUUM 开销。 很少使用的数据可以迁移到更便宜、更慢的存储介质上。
WaitLatch(MyLatch, WL_LATCH_SET,0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); /* 进程被唤醒 */ ResetLatch(MyLatch); /* 如果进程是因为死锁超时被唤醒,那么检测死锁 */ if(got_deadlock_timeout) { CheckDeadLock(); got_deadlock_timeout =false; ...
DELETE CASCADE –show you how to automatically delete rows in child tables when the corresponding rows in the parent table are deleted. CHECK constraint –add logic to check value based on a Boolean expression. UNIQUE constraint –ensure that values in a column or a group of columns are unique...