![]() ![]() The result set now is sorted by the AlbumId column in ascending order as shown in the screenshot. Suppose you want to sort the result set based on AlbumId column in ascending order, you use the following statement: SELECT name,Īlbumid ASC Code language: SQL (Structured Query Language) ( sql ) The SELECT statement that does not use ORDER BY clause returns a result set that is not in any order. Tracks Code language: SQL (Structured Query Language) ( sql ) Suppose, you want to get data from name, milliseconds, and album id columns, you use the following statement: SELECT name, Let’s take the tracks table in the sample database for the demonstration. You can sort the result set using a column that does not appear in the select list of the SELECT clause. Then, it sorts the sorted rows using the second column, and so on. In other words, the ORDER BY clause sorts the rows using the first column in the list. The ORDER BY clause sorts rows using columns or expressions from left to right. In case you want to sort the result set by multiple columns, you use a comma (,) to separate two columns. In other words, it sorts the result set in the ascending order by default. If you don’t specify the ASC or DESC keyword, SQLite sorts the result set using the ASC option. In this syntax, you place the column name by which you want to sort after the ORDER BY clause followed by the ASC or DESC keyword. It allows you to sort the result set based on one or more columns in ascending or descending order. The ORDER BY clause comes after the FROM clause. To sort the result set, you add the ORDER BY clause to the SELECT statement as follows: SELECTĬolumn_2 DESC Code language: SQL (Structured Query Language) ( sql ) If you use the SELECT statement to query data from a table, the order of rows in the result set is unspecified. It means that the rows in the table may or may not be in the order that they were inserted. SQLite stores data in the tables in an unspecified order. Coordinate this activity with the database administrators (DBAs) and make a backup of the original statistics.Summary: in this tutorial, you will learn how to sort a result set of a query using SQLite ORDER BY clause. That might, however, also lead to unwanted side effects. My personal recommendation goes even further: after every index change, update the statistics for the base table and all its indexes. Such statistics will enable Oracle Database to correctly decide when to use the index. For this reason, the Oracle documentation recommends updating the table statistics after creating a function-based index:Īfter creating a function-based index, collect statistics on both the index and its base table using the DBMS_STATS package. Although the Oracle database collects the index statistics for new indexes automatically ( since release 10 g), it does not update the table statistics. Statistics for a function-based index (FBI) are also kept on table level as virtual columns. These figures are reused if a column is part of multiple indexes. The Oracle database maintains the information about the number of distinct column values as part of the table statistics. There are no dedicated operations or keywords for function-based indexes. The database traverses the B-tree and follows the leaf node chain. It is a regular INDEX RANGE SCAN as described in Chapter 1. Index Cond: (upper((last_name)::text) = 'WINAND'::text) Recheck Cond: (upper((last_name)::text) = 'WINAND'::text) |*2 | INDEX RANGE SCAN | EMP_UP_NAME | 40 | 1 |Ģ - access(UPPER("LAST_NAME")='WINAND') PostgreSQL QUERY PLAN | 1 | TABLE ACCESS BY INDEX ROWID| EMPLOYEES | 100 | 41 | See “ Full Table Scan” to see why that might make sense. This causes the optimizer to ignore the index and do a TBSCAN. When using UPPER('winand'), the optimizer does a gross misestimation and expects 4% of the table rows to be selected. ![]() The query was changed to WHERE UPPER(last_name) = 'WINAND' (no UPPER on the right hand side) to get the expected result. From the database’s perspective, that’s something entirely different.Ģ | FETCH EMPLOYEES | 1 of 1 (100.00%) | 13ģ | IXSCAN EMP_UP_NAME | 1 of 10000 (. Although there is an index on LAST_NAME, it is unusable-because the search is not on LAST_NAME but on UPPER(LAST_NAME). It is a return of our old friend the full table scan. Predicate Information (identified by operation id):ġ - filter(UPPER("LAST_NAME")='WINAND') PostgreSQL QUERY PLANįilter: (upper((last_name)::text) = 'WINAND'::text) |* 1 | TABLE ACCESS FULL| EMPLOYEES | 10 | 477 |
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