![]() ![]() | INDEX FULL SCAN DESCENDING| SALES_DT_PR | 10 | 3 | | TABLE ACCESS BY INDEX ROWID| SALES | 1004K| 9 | In this particular example, one might suspect that this must be a top-N query because of the sudden drop of the row count estimate that cannot explained by any filtering predicates (Predicate Information section is empty). The top-N behaviour is not directly visible in the DB2 execution plan unless there is a SORT operation required (then the last_explained view indicates it in brackets: SORT (TOP-N), see next example). Starting with release 2012, SQL Server supports the fetch first extension as well.Īll of the above shown SQL queries are special because the databases recognize them as top-N queries.ģ | IXSCAN (REVERSE) SALES_DT_PR | 1009326 of 1009326 | 2624 SQL Server provides the top clause to restrict the number of rows to be fetched. The previously used limit clause still works as shown in the MySQL example. PostgreSQL supports the fetch first extension since version 8.4. To use this column in a filter, we have to wrap the query: SELECT * With earlier releases you have to use the pseudo column ROWNUM that numbers the rows in the result set automatically. The Oracle database introduced the fetch first extension with release 12c. MySQL and PostgreSQL use the limit clause to restrict the number of rows to be fetched. The proprietary limit keyword is supported since DB2 LUW 9.7 (requires db2set DB2_COMPATIBILITY_VECTOR=MYS). (Steven and Lucy have the same last name, so their order is determined by first name.) Michael is 22, which makes him the next-oldest student and last of the three rows returned.DB2 supports the standard’s fetch first syntax since version 9 at least (LUW and zOS). Lucy is now first because her first name comes before Steven’s. However, Mary is omitted because she is the first row and the offset is 1 (i.e. If you look at the table, you’ll see that the oldest students (Steven, Lucy, Mary) are 25 years old. It then sorts by last_name and first_name in ascending order. This query first sorts rows according to the age column in descending order. We use the offset value to start on the second returned row and limit the results to three rows: first_name Here, we’re first ordering the rows by age (descending), then last name, then first name. If you’d like to select three rows from a sorted result set, use ORDER BY: In these queries, the result rows are unordered. The query returns the same records as the previous query because the offset is zero. The offset and the number of rows are separated by a comma. ‘0’ is the first row, 1 is the second row, etc.). It indicates the position of the first row returned by LIMIT (i.e. LIMIT’s optional OFFSET argument is placed before the argument indicating the number of returned rows. Unless you specify otherwise with the OFFSET argument, this function will always return the first n rows that meet query requirements. In our example, LIMIT 3 produced a result set containing three rows. The only required argument is the number of rows to display. ![]() (Even ORDER BY should be listed before LIMIT.) It is used in the SELECT statement, usually at the end of the statement. The LIMIT clause limits the number of rows in the result set. Let’s select students’ full names and ages, but limit the rows returned to three. Our database has a table named student with data in the columns id, first_name, last_name, and age. You’d like to limit the number of rows in a result set in MySQL. ![]()
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