rownum

对于 Oracle 的 rownum 问题，很多资料都说不支持>,>=,=,between...and，只能用以上符号(<、<=、!=)，并非说用>,>=,=,between..and 时会提示SQL语法错误，而是经常是查不出一条记录来，还会出现似乎是莫名其妙的结果来，其实您只要理解好了这个 rownum 伪列的意义就不应该感到惊奇，同样是伪列，rownum 与 rowid 可有些不一样，下面以例子说明 假设某个表 t1(c1) 有 20 条记录 如果用 select rownum,c1 from t1 where rownum < 10, 只要是用小于号，查出来的结果很容易地与一般理解在概念上能达成一致，应该不会有任何疑问的。 可如果用 select rownum,c1 from t1 where rownum > 10 (如果写下这样的查询语句，这时候在您的头脑中应该是想得到表中后面10条记录)，你就会发现，显示出来的结果要让您失望了，也许您还会怀疑是不谁删了一 些记录，然后查看记录数，仍然是 20 条啊？那问题是出在哪呢？ 先好好理解 rownum 的意义吧。因为ROWNUM是对结果集加的一个伪列，即先查到结果集之后再加上去的一个列 (强调：先要有结果集)。简单的说 rownum 是对符合条件结果的序列号。它总是从1开始排起的。所以你选出的结果不可能没有1，而有其他大于1的值

I am trying to execute a query like select * from tableName where rownum=1 This query is basically to fetch the column names of the table.There are more than million records in the table.When I put the above condition its taking so much time to fetch the first row.Is there any alternate to get the first row. Try this: select * from tableName where rownum<=1 There are some weird ROWNUM bugs, sometimes changing the query very slightly will fix it. I've seen this happen before, but I can't reproduce it. Here are some discussions of similar issues: http://jonathanlewis.wordpress.com/2008/03/09

THe HSQLDB changelog states that ROWNUM() was added in v2.2.0 which I am using without any problems when running integration tests against the in-memory HSQLDB. However I want to run the same tests against a real Oracle 10g database, but the query fails because the pseudo-column is called ROWNUM . Is there an easy way write a single query string that works in both environments? The ROWNUM() function is available by default in HSQLDB 2.2.x and later. If you enable Oracle syntax compatibility mode, you can also use ROWNUM. This statement enables it: SET DATABASE SQL SYNTAX ORA TRUE Or use the

I have a table that will have millions of records. I want to make sure Oracle stops looking as long as it finds its first match. select * from table1 where table1.column1 = 'somevalue' AND table2.column2 = 'somevalue' AND rownum = 1 I heard about that Oracle will fetch ALL the rows that meet the criteria on column1 and column2 and then only apply the rownum filter to get the first row, which defeats the purpose. Run an explain plan on the query, and you'll find that you heard wrong -- Oracle will apply the rownum predicate as soon as a row is identified as part of the result set based on the

I'm using oracle to output line items in from a shopping app. Each item has a quantity field that may be greater than 1 and if it is, I'd like to return that row N times. Here's what I'm talking about for a table product_id, quanity 1, 3, 2, 5 And I'm looking a query that would return 1,3 1,3 1,3 2,5 2,5 2,5 2,5 2,5 Is this possible? I saw this answer for SQL Server 2005 and I'm looking for almost the exact thing in oracle. Building a dedicated numbers table is unfortunately not an option. I've used 15 as a maximum for the example, but you should set it to 9999 or whatever the maximum quantity

How to add an offset in a "select" query in Oracle 11g. I only know how to add the limit by e.g rownum <= 5 this question is not a duplicate, I already checked the other questions and are not related to mine. So, how to add the offset in Oracle 11g ? Lalit Kumar B You can do it easily on 12c by specifying OFFSET . In 12c , SELECT val FROM table ORDER BY val OFFSET 4 ROWS FETCH NEXT 4 ROWS ONLY; To do the same on 11g and prior, you need to use ROWNUM twice, inner query and outer query respectively. The same query in 11g , SELECT val FROM (SELECT val, rownum AS rnum FROM (SELECT val FROM table