二十四、用其他表中的值更新
db2/mysql
update emp e set(e.sal,e.comm)=(select ns.sal,ns.sal/2 from new_sal ns where ns.deptno=e.deptno) where exists(select nul from new_sa ns where ns.deptno=e.deptno)

oracle
update(select e.sal as emp_sal,e.comm as emp_comm,ns.sal as ns_sal,ns.sal/2 as ns_comm frm emp e,new_sal ns where e.deptno=ns.deptno) set emp_sal=ns_sal,emp_comm=ns_comm

postgresql
update emp set sal=ns.sal,comm=ns.sal/2 from new_sal ns where ns.deptno=emp.deptno

sqlserver
update e set e.sal=ns.sal,e.comm=ns.sal/2 from emp e,new_sal ns where ns.deptno=emp.deptno

二十五、合并记录
oracle
merge into emp_commission ec using(select * from emp) emp on(ec.empno=emp.empno) when matched then update set ec.comm=1000 delete where (sal<2000) when not matched then insert (ec.empno,ec.ename,ec.deptno,ec.comm) values (emp.empno,emp.ename,emp.deptno,emp.comm)

二十六、删除违反参照完整性的记录
delete from emp where not exists(select * from dept where dept.deptno=emp.deptno)

delete from emp where deptno not in(select deptno from dept)

二十七、删除重复记录
delete from dupes where id not in (select min(id) from dupes group by name(需要判断重复的字段))

二十八、删除从其他表引用的记录
delete from emp where deptno in (select deptno from dept_accidents group by deptno having count(*)>=3)

（以下模式名schema为smeagol）
二十九、列出模式中的表
db2
select tabname from syscat.table where tabschema='smeagol'

oracle
select table_name from all_tables where owner='smeagol'

postgresql/mysql/sqlserver
select tablename from information_schema.tables where table_schema='smeagol'

三十、列出表的列
db2
select colname,typename,colno from syscat.columns where tablename='emp' and tabschema='smeagol'

oracle
select column_name,data_type,column_id from all_tab_columns where owner='smeagol' and table_name='emp'

postgresql/mysql/sqlserver
select column_name,data_type,ordinal_position from information_schema='smeagol' and table_name='emp'

三十一、列出表的索引列
db2
select a.tabname,b.indname,b.colname,b.colseq from syscat.indexes a,syscat.indexcoluse b where a.tabname='emp' and a.tabschema='smeagol' and a.indschema=b.indschema and a.indname=b.indname

oracle
select table_name,index_name,column_name,column_position from sys.all_ind_columns where table_name='emp' and table_owner='smeagol'

postgresql
select a.tablename,a.indexname,b.column_name from pg_catalog.pg_indexes a,information_schema.columns b where a.schemaname='smeagol' and a.tablename=b.table_name

mysql
show index from emp

sqlserver
select a.name table_name,b.name index_name,d.name column_name,c.index_column_id from sys.tables a,sys.indexes b,sys.index_columns c,sys.columns d where a.object_id=b.object_id and b.object_id=c.object_id and b.index_id=c.index_id and c.object_id=d.object_id and c.column_id=d.column_id and a.name='emp'

三十二、列出表约束
db2
select a.tabname,a.constname,b.colname,a.type from syscat.tabconst a,syscat.columns b where a.tabname='emp' and a.tabschema='smeagol' and a.tabname=b.tabname and a.tabschema=b.tabschema

oracle
select a.table_name,a.constraint_name,b.column_name,a.constraint_type from all_constraints a,all_cons_columns b where a.table_name='emp' and a.owner='smeagol' and a.table_name=b.table_name and a.owner=b.owner and a.constraint_name=b.constraint_name

postgresql/mysql/sqlserver
select a.table_name,a.constraint_name,b.column_name,a.constraint_type from information_schema.table_constraints a,information_schema.key_column_usage b where a.table_name='emp' and a.table_schema='smeagol' and a.table_name=b.table_name and a.table_schema=b.table_schema and a.constraint_name=b.constraint_name

三十三、列出没有相应索引的外键
db2
select fkeys.tabname,fkeys.constname,fkeys.colname,ind_cols.indname from (select a.tabschema,a.tabname,a.constname,b.colname from syscat.tabconst a,syscat.keycoluse b where a.tabname='emp' and a.tabsche