select id, date, another_info from ( select id, date, another_info, row_number() over (partition by id order by date desc) as rn from the_table ) t where rn = 1 order by id; The solution with a window function is in most cases faster than using a sub-query. 机译 假设我有下...
test=# select currval('tbl_serial_a_seq'); currval --- 1 (1 row) 示例2:获取最近一次使用nextval的返回值 test=# select nextval('sql_tbl_serial2_a'); nextval --- 5 (1 row) test=# select lastval(); lastval --- 5 (1 row) test=# select nextval('tbl_serial_a_seq'); nextval...
SQL> SELECT first_name, last_name, start_date 2 FROM s_emp 3 WHERE start_date BETWEEN ’09-may-91’ 4 AND ’17-jun-91’; 例2: SQL> SELECT last_name 2 FROM s_emp 3 WHERE last_name LIKE ’_a%’; //显示所有第二个字母为 a的last_name 例3: 如果有列为NULL SQL> SELECT id, ...
ACCESS SHARE锁:select语句都会在表上请求该锁。 ACCESS EXCLUSIVE锁:alter table、drop table、truncate、reindex、cluster、VACUUM FULL、LOCK TABLE命令会向postgreSQL请求该锁。 ROW SHARE锁:select ... for update和select... for share会请求该锁。 ROW EXCLUSIVE锁:UPDATE、DELETE、INSERT命令会在所修改的表上请...
CREATEORREPLACEFUNCTION"public"."func1"()RETURNSSETOF"public"."a"AS$BODY$BEGINreturnquery select a.id,a.name from a limit2;return;END$BODY$LANGUAGEplpgsqlSTABLECOST100ROWS1000 得到的结果如下图。 期中return query还可以使用return next。具体语法是: ...
select tfun1(); postgres=# select tfun1(); NOTICE: curs1 : China NOTICE: curs1 : USA NOTICE: curs2 : 1 NOTICE: curs2 : 2 NOTICE: curs3 : New York NOTICE: curs3 : Bostom tfun1 --- 0 (1 row) 3 使用游标(方法一) 3.1 fetch 总结速查:LAST语法直接转义到最后一行;RELATIVE语法...
[ ALL | DISTINCT ] select ] [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ] [ LIMIT { count | ALL } ] [ OFFSET start [ ROW | ROWS ] ] [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ] [ FOR { UPDATE | ...
SELECTd.department_name"部门名称",concat(e.first_name,',',e.last_name)"姓名",e.salary"月薪",ROW_NUMBER()OVER(PARTITIONBYe.department_idORDERBYe.salaryDESC)AS"row_number",RANK()OVER(PARTITIONBYe.department_idORDERBYe.salaryDESC)AS"rank",DENSE_RANK()OVER(PARTITIONBYe.department_idORDERBYe....
RRR: row number,记录的行编号 接着看一个 rowid的示例,如下: SELECT ROWID, last_name FROM employees WHERE department_id = 20; ROWID LAST_NAME --- --- AAAAaoAATAAABrXAAA BORTINS 得到的结果是18位的字符,可使用Oracle的dbms_rowid包的相关函数对rowid的四部分进行解析,生成可读的Data object numbe...
postgres=# select pg_relation_filepath('ssss');pg_relation_filepath---base/13591/40976(1 row) 如果是空表,那么40976这个文件的状态是empty,如果此表有数据,那么将是data(一开始是空的,后面我添加了数据,添加数据没有演示): [root@EULER1 13591]# pwd/usr...