Contents
Is there a problem with Fetch first row only?
If the query was supposed to return one row, and it instead returned thousands, it would have been obvious that there was a problem with the query. The moral of the story here is that when queries are using “FETCH FIRST ROW ONLY”, you may want to take an extra careful look to see if they are processing more rows than they have to.
Why do I Only Want the first 1 rows?
Letting the database know your “intentions” (eg “I only want the first x rows”) can be critical to performance. For example, normal sorting operations store the entire result set in memory or on disk in temporary tablespace. But with the FETCH clause Oracle knows it only has to track the Top N rows and can use significantly less memory for sorting.
Do you have to use fetch first n rows only in MySQL?
However, if you or the system is not sure, then it is an extra safeguard. Depending on the optimizer settings (or mood or statistics or metadata), the additional syntax may help with performance.
How to fetch first row in Oracle Database?
I have a cursor in oracle database which would be fetching thousands of rows in a sorted manner but I would actually need only the first row (i.e., oldest one first). The loop is designed in such a way that it processes first one row and comes out. And then the cursor is opened again to fetch the remaining rows.
When to use next instead of fetch in Oracle?
The FETCH clause specifies the number of rows or percentage of rows to return. For the semantic clarity purpose, you can use the keyword ROW instead of ROWS, FIRST instead of NEXT. For example, the following clauses behavior the same: The ONLY returns exactly the number of rows or percentage of rows after FETCH NEXT (or FIRST ).
How to limit rows returned by Oracle fetch?
The following query returns top 5% products with the highest inventory level: The inventories table has 1112 rows, therefore, 5% of 1112 is 55.6 which is rounded up to 56 (rows). The following query skips the first 10 products with the highest level of inventory and returns the next 10 ones:
How to fetch catentrel from first row only?
SELECT CATENTREL.CATENTRY_ID_CHILD FROM CATENTREL INNER JOIN CATENTDESC ON (CATENTREL.CATENTRY_ID_CHILD = CATENTDESC.CATENTRY_ID) INNER JOIN CATENTRY ON (CATENTRY.CATENTRY_ID = CATENTDESC.CATENTRY_ID) , CATGPENREL WHERE CATENTREL.CATENTRY_ID_PARENT = ?