Discreet cam site - Concatenating field field oracle third two updating

As you can see this new function is very handy and behaves much different that the old form of concatenation.

Instead of evaluating to NULL if any if the columns contain NULL values, the CONCAT() function replaces it with an empty string.

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If not, the index tree cannot help find that place. We can take advantage of the fact that the first index column is always usable for searching.

Again, it is like a telephone directory: you don't need to know the first name to search by last name. SUBSIDIARY_ID = 00002.) ---- ----------- ------ --------- --------- ------ ------- | id | table | type | key | key_len | rows | Extra | ---- ----------- ------ --------- --------- ------ ------- | 1 | employees | ref | PRIMARY | 5 | 123 | | ---- ----------- ------ --------- --------- ------ ------- -------------------------------------------------------------- |Id |Operation | Name | Rows | Cost | -------------------------------------------------------------- | 0 |SELECT STATEMENT | | 106 | 75 | | 1 | TABLE ACCESS BY INDEX ROWID| EMPLOYEES | 106 | 75 | |*2 | INDEX RANGE SCAN | EMPLOYEE_PK | 106 | 2 | -------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("SUBSIDIARY_ID"=20)In general, a database can use a concatenated index when searching with the leading (leftmost) columns.

The database considers each column according to its position in the index definition to sort the index entries.

The first column is the primary sort criterion and the second column determines the order only if two entries have the same value in the first column and so on.

This achieves the same as using the CONCAT() function, but requires a lot more code and readability.

The next set of code is using the new CONCAT() function, new to SQL Server 2012.

Note that the column order of a concatenated index has great impact on its usability so it must be chosen carefully.

For the sake of demonstration, let's assume there is a company merger.

Database administrators are in a similar position as they might know the database schema but do not have deep insight into the access paths.


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