Subquery Factoring, 其实就是平常比较熟悉的With语句,Adrian Billington 在他的网站上写了一篇介绍Subquery Factoring很好的文章,见这里。这篇Blog同样是对他的这篇文章的笔记。 With语句一般有两种用途,一种就是用来把复杂的SQL语句简单化:复杂的SQL语句一般都会嵌套很多层次,无论是写起来还是读起来都很困难,通过用Wit...
Case Statement 相当于一组IF…THEN…ELSE…END IF语句,不需要返回值,只是在条件匹配的时候执行某种操作而已,所以在每个WHEN…THEN之后需要有一个分号,表示一条执行语句! CASE {variable or expression} WHEN {value} THEN {one or more operations};[WHEN..THEN] ELSE {default operation};ENDCASE; CASE WHEN ...
The subquery will perform a COUNT function using a CASE statement to determine if the returned value is Y or N depending on the value of COUNT. It is calculated for each product_id and matches the outer query. This will result in the active column for some products set to Y and others ...
1.如果在RANKing中有多个分区，那么在每个分区中都会有排在第一位的行，并且CASE表达式期望从子查询中返...
带有连接的Oracle SQL case语句产生奇怪的结果[duplicate]这是意料之中的，我会说，因为一个名字排除另...
SQL macros and WITH clause are not known to be great friends: you cannot call a SQL macro in a WITH clause and if you want to define a table macro returning a query containing a WITH subquery(ies), then you won’t be able to use scalar parameters in this subquery. In theprevious po...
subquery:It refers to the sub-query which is a SELECT statement and it is query within another query. How EXISTS work in Oracle? This function is used with a sub query to evaluate whether any row is returned by the sub-query. So when we execute the query the sub-query is executed fir...
1.如果在RANKing中有多个分区，那么在每个分区中都会有排在第一位的行，并且CASE表达式期望从子查询中...
If you’ve looked at the example on the Oracle Developer Forum you will have seen that there’s an SQL statement that references a stored view and the factored subquery of interest is defined in the view. This means we might be able to edit the query that calls the view to include a ...
The SQL used to gather index stats from any of the calls to dbms_stats.gather_xxx_stats() does a simple select statement that is hinted to access the index. In my case the indexes were all fairly small – smaller than the critical number of blocks that trigger sampling methods –so Ora...