first_value(value any) 返回第一值 postgres=# select first_value(amount) over(partition by begincity order by id),* from bills; first_value | id | goodsdesc | beginunit | begincity | pubtime | amount ---+---+---+---+---+---+--- 1915.86 | 1 | 衣服| 海南省 | 三亚市 |...
SELECTfirst_name,last_name,salaryFROMemployeesorderbysalarydescOFFSET10ROWSfetchfirst10rowsonly; OFFSET表示先忽略掉多少行数据,然后再返回后面的结果。ROWS也可以写成ROW。对于应用程序而言,只需要传入不同的OFFSET偏移量和FETCH数量,就可以在结果中任意导航。使用LIMIT加上OFFSET同样可以实现分页效果: SELECTfirst_name...
3,row_number() OVER()对分组后的数据标注行号,从1开始。 postgres=#SELECTrow_number()OVER(PARTITIONBYsubjectORDERBYscoreDESC),*FROMscores; row_number|id|subject|stu_name|score---+---+---+---+---1|2|Chinese|user2|902|3|Chinese|user3|903|1|Chinese|user1|801|8|English|user2|902|7|...
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, ...
select id into a from test; 方式二:动态命令 代码语言:javascript 代码运行次数:0 运行 AI代码解释 EXECUTEcommand-string[INTO[STRICT]target][USINGexpression[,...]]; 举个例子,如下: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 --和上面一样,把id的值查询出来赋值给a ...
[ 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 | ...
(1 row) 1. 2. 3. 4. 5. 可见string_agg函数将输出的结果集连接成了字符串,并 ]用指定的逗号分隔符分隔,回到本文开头的问题,通过SQL实现,如下所示: mydb=> SELECT country,string_agg(city,',') FROM city GROUP BY country; country | string_agg ...
1 row)total_cost = io_cost + cpu_cost = 30811, 刚好等于explain语句输出的cost(cost=0.00..30811.00 rows=2000000 width=12)。不同扫描算子的代价对比 接下来我们通过同一个SQL select * from t1 where a <= 10000; 的不同执行计划的代价，来理解扫描算子的过程。顺序扫描 xiaoming=# explain select...
SELECTfirst_name,last_name,salaryFROMemployeesWHEREsalary=10000ANDlast_name='King';first_name|last_name|salary---+---+---Janette|King|10000.00(1row) OR运算符的逻辑真值表如下: OR逻辑或运算符只要有一个条件为真,结果就为真。以下查询返回薪水为 10000,或者姓氏为“King”的员工: SELECTfirst_name...
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....