The same applies to keywords as they are allowed to be entered in any case, but most of the time, it is a good practice to use them in all upper cases according to conventions.Īlternatively, the collation property for SQL database server can also be checked by querying on the table named databases that are present in the sys database of your SQL server to check for the case sensitivity that is allowed for the particular database by mentioning the value of the name column as the value of your database name for which you are checking the collation. In the above output, we can observe that the collation value contains CI that is case sensitive, and hence while querying on that database server, the objects other than keywords can be specified in upper or lower case. They stand for case insensitive and case sensitive, respectively. The collation value contains either CI or CS in it. The output of the execution of the above query statement is as follows – SELECT Serverproperty('COLLATION') AS COLLATION In this topic, we are going to learn about SQL ignore-case. In this article, we will learn how we can check for the assigned collation values that determine case sensitivity of SQL and further see how lower and upper functions are used to make the queries that ignore the case of the values of the columns while searching or applying restriction. The COLLATION is the property that decides and helps us to specify whether the elements other than keywords in SQL are to be allowed for case insensitivity or not. The names of the tables and columns specification are set to case insensitive on the SQL database server however, it can be enabled and disabled by configuring the settings in SQL. SQL keywords are by default set to case insensitive, which means that the keywords are allowed to be used in lower or upper case. Coordinate this activity with the database administrators (DBAs) and make a backup of the original statistics.SQL Case sensitivity is to use the query statements and the keywords tables and columns by specifying them in capital or small letters of alphabets. 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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