This is just a short note the point out that RECORD option of TKPROF is extremely useful in recording and capturing the non-recursive SQL statements in the order of execution from the SQL trace file. I have not had a requirement to use it until—today—one of my developers lost the original test script used when [...]
SET TIMING—one of the most frequently used commands—displays timing statistics on each SQL command or PL/SQL block. What if you want to collect timing statistics for multiple group of statements? TIMING command becomes handy in such situation—one of things that I knew and have forgotten over time. It can be used to collect data to do [...]
I noticed a strange behavior—a SQL statement, which used to return no rows in the past, started returning rows in an environment where the test data set has not changed. I performed a code comparison and observed a difference in the order of a table in FROM clause. After looking through, I found a bug entry on MOS [...]
Earlier I posted a list of operations and options available in Oracle database as of 11g R2, you should note that not all options are available for each operation. This post covers, over 200, commonly observed row source operations—unique combination of operations and options—each post contains a sample script to produce the operation and some may contain hints and [...]
OVERLAPS predicate is a useful feature, which is not available in most SQL implementations that can help to determine whether the two periods overlap each other. If two periods overlap then the predicate evaluates to TRUE otherwise FALSE. Let us create a test table with three rows – one with overlapping dates, second with non-overlapping [...]
The SQL standard allows you to use an inline view in a DELETE statement, see the pseudo form below – If a condition such as key-preserved table is not met then it will result in error, “ORA-01752: cannot delete from view without exactly one key-preserved table.” I would like to show you the caveat of [...]
Joins A join is a query that combines rows from two or more tables. Oracle performs a join whenever multiple tables appear in the FROM clause of the query. Below is a SQL join statement, legacy syntax and ANSI/ISO syntax (also referred as new join syntax, was first introduced in Oracle 9i release) in a [...]
Access paths are ways in which data is retrieved from the database. In general, index access paths should be used for statements that retrieve a small subset of table rows, while full scans are more efficient when accessing a large portion of the table. Online transaction processing (OLTP) applications, which consist of short-running SQL statements [...]
CREATE TABLE has lot of option to go with it; it is hard to remember all of them. Most people will get lost while reading the rail road diagrams. It is fairly quick to create the table in its simple form and obtain all the parameters associated with it. Once the table is created in [...]
The advantages of using bitmap indexes are greatest for low cardinality columns: that is, columns in which the number of distinct values is small compared to the number of rows in the table. If the number of distinct values of a column is less than 1% of the number of rows in the table, or if the values in a column are repeated more than 100 times, then the column is a candidate for a bitmap index. Even columns with a lower number of repetitions and thus higher cardinality can be candidates if they tend to be involved in complex conditions in the WHERE clauses of queries.
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