-- rows between unbounded preceding and current row 包括本行和该分组内之前所有的行 -- rows between current row and unbounded following 包括本行和该分组内之后所有行 -- rows between 5 preceding and 1 following 包括前五行和后一行 -- over (order by x) 相当于 over(order by x rows between un...
I have created two test tables below with two rows in each table. I have then placed the table names in a temp table. I'm trying to loop through the two test tables and get a count of each and insert into another table with the table names and counts. ...
EXPLAIN ANALYZE SELECT e.emp_id, e.emp_name FROM employee e JOIN (SELECT dept_id, AVG(salary) AS dept_average FROM employee GROUP BY dept_id) t ON e.dept_id = t.dept_id WHERE e.salary > t.dept_average;-> Nested loop inner join (actual time=0.722..2.354 rows=6 loops=1) ->...
in是把外表和内表作hash连接,而exists是对外表作loop循环,每次loop循环再对内表进行查询,一直以来认为exists比in效率高的说法是不准确的。 如果查询的两个表大小相当,那么用in和exists差别不大;如果两个表中一个较小一个较大,则子查询表大的用exists,子查询表小的用in; 例如:表A(小表),表B(大表) 代码语...
in/exists 对比in 是把外表和内表作 hash 连接,而 exists 是对外表作 loop 循环,每次 loop 循环再对内表进行查询;如果查询语句使用了 not in 那么内外表都进行全表扫描,没有用到索引;而 not extsts 的子查询依然能用到表上的索引;所以无论那个表大,用 not exists 都比 not in 要快。
dbms_output.put_line('输出数字:'||v_i);--输出1到100以内的自然数v_i:=v_i+1;--改变循环变量的值endloop;end;--需求:输出部门表的所有内容?--into只能用一个或者一行的方式赋值,我们可以用bulk collect into来给行类型变量整体赋值,也就是说可以一次性--把所有数据查询出来,为table类型的变量赋值。
CREATE TABLE TestBatch (ColA INT PRIMARY KEY, ColB CHAR(3)); GO INSERT INTO TestBatch VALUES (1, 'aaa'); INSERT INTO TestBatch VALUES (2, 'bbb'); INSERT INTO TestBatch VALUSE (3, 'ccc'); -- Syntax error. GO SELECT * FROM TestBatch; -- Returns no r...
FORdateINlist_of_dates LOOP INSERTINTOfinal_table(date, revenue_mtd) SELECT@dateasdate,sum(revenue)asrevenue_mtd FROMsales WHEREsales.dtbetweendate_trunc('month',@date)and@date; ENDLOOP; 所以支持游标循环的数据库是比较方便做一些函数式编程的。
filter out rows in table data which have non-english characters Find a database size limit from within the SQL Server Find a String inside nvarchar(max) Find all rows where the value in one column only occurs once Find All Special Characters in a SQL Server Find and insert missing records...
1.select子句中尽量避免使用* select子句中，*是选择全部数据的意思。比如语句：“select * from 成绩表...