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Problem:You want to define a function in Oracle using WITH clause.SolutionStarting with Oracle Database 12.1, you can define functions as well as procedures within the same SQL statement in which the SELECT statement appears. This allows the context switch between the PL/SQL and SQL engines by allowing both steps to take place in the SQL engine and, in turn, provides for a performance gain.The function or procedure needs to be defined using the WITH clause. Remember, In previous versions of the Oracle platform, only subqueries could be defined in the WITH clause.ExampleWITH FUNCTION func_amount(p_emailid IN VARCHAR2) RETURN NUMBER IS l_amt ... Read More
Problem:You want to capture Oracle errors in PL/SQL.SolutionAll Oracle errors can be trapped with the help of the OTHERS exception handler. Let us take an example. We will be using students table to demonstrate the usage.Let us first look at the table structure.ExampleDESC students;OutputName Null Type ------------- -------- ------------ STUDENT_ID NUMBER(6) FIRST_NAME VARCHAR2(20) LAST_NAME NOT NULL VARCHAR2(25) EMAIL NOT NULL VARCHAR2(40) PHONE_NUMBER VARCHAR2(20) JOIN_DATE ... Read More
Problem:You want to generate JSON data and perform Schema Validation in Oracle.SolutionFunctions like JSON_OBJECT, JSON_ARRAYAGG, JSON_QUERY can be used to generate a complex json data using mutiple columns and tables.JSON_OBJECT:- Its an SQL/JSON function. JSON_OBJECT takes as its input one or more property key-value pairs. It returns a JSON object that contains an object member for each of those key-value pairs.JSON_ARRAYAGG:-The SQL/JSON function JSON_ARRAYAGG is an aggregate function. It takes as its input a column of SQL expressions, converts each expression to a JSON value, and returns a single JSON array that contains those JSON values.JSON_QUERY:-JSON_QUERY finds one or more ... Read More
Problem:You want to use datetime functions to extract or process datetimes.SolutionADD_MONTHS()ADD_MONTHS(x, y) returns the result of adding y months to x. If y is negative, then y months are subtracted from xExample-- add 12 months SELECT ADD_MONTHS('01-JAN-2020', 12) FROM dual;Output-- 01/JAN/21Example-- subtract 12 months SELECT ADD_MONTHS('01-JAN-2020', -12) FROM dual;Output-- 01/JAN/21We can provide a time and date to the ADD_MONTHS() function.ExampleSELECT ADD_MONTHS(TO_DATE('01-JAN-2020 01:01:01', 'DD-MON-YYYY HH24:MI:SS'), 2) FROM dual;Output-- 01/MAR/20LAST_DAY()LAST_DAY(x) returns the date of the last day of the month part of x.ExampleSELECT LAST_DAY('01-JAN-2020') FROM dual;Output-- 31/JAN/20MONTHS_BETWEEN()MONTHS_BETWEEN(x, y) returns the number of months between x and y. If x occurs before y ... Read More
Problem:You want to insert dates into a table and retrieve them.SolutionOracle, by default the uses the format DD-MON-YYYY to represent a date, whereDD represents a two-digit day.MON represents first three letters of the month, e.g., FEB.YYYY is a four-digit year, e.g., 1968Let us take a look at an example of adding a row to the customers table, which contains a DATE column named dob.The following INSERT adds a row to the customers table, setting the dob column to 05-FEB-1968:ExampleINSERT INTO customers ( customer_id, first_name, last_name, dob, phone) VALUES (7, 'James', 'Bond', '31-DEC-2000', '007-007-0007');You can also use the DATE keyword to ... Read More
Problem:You want to UNPIVOT results in Oracle.SolutionThe UNPIVOT clause is new for Oracle Database 11g and enables you to flip the columns into rows in the output from a query, and, at the same time, allow you to run an aggregation function on the data.Consider a table called customer which has below data stored inside.ExampleSELECT * FROM customers;Output1 tammy.bryant@internalmail Tammy Bryant 2 roy.white@internalmail Roy White 3 gary.jenkins@internalmail Gary Jenkins 4 victor.morris@internalmail Victor Morris 5 beverly.hughes@internalmail Beverly HughesIn the customer table we can see that full name has First name and last ... Read More
Problem:You want to PIVOT results in Oracle.SolutionThe PIVOT clause is new for Oracle Database 11g and enables you to flip the rows into columns in the output from a query, and, at the same time, allow you to run an aggregation function on the data.PIVOT is especially useful to look at overall trends in large amounts of data.We will be using sales data to demonstrate the usage.ExampleSELECT * FROM sales;Output12008 12 1998-02-28 6 37 552 1898.88 12008 18 1998-02-28 6 37 463 1592.72 12008 20 1998-02-28 6 37 2430 8359.2 12008 25 ... Read More
Problem:You want to monitor the usage of the temporary tablespace in Oracle.Solution:We can use the following query to find out the used and free space in a temporary tablespace.We will begin with identifying temporary table space names.ExampleSELECT tablespace_name FROM dba_tablespaces WHERE contents = 'TEMPORARY';OutputTEMPNext up we will use below SQL to identify the used and free space in temporary tablespace.ExampleSELECT * FROM (SELECT a.tablespace_name, SUM(a.bytes/1024/1024) allocated_mb FROM dba_temp_files a WHERE a.tablespace_name = 'TEMP' GROUP BY a.tablespace_name ) x, (SELECT SUM(b.bytes_used/1024/1024) used_mb, SUM(b.bytes_free /1024/1024) free_mb FROM v$temp_space_header b ... Read More
Problem:You want to find out the recent important waits in your database, as well as the users, SQL statements, and objects that are responsible for most of those waits.SolutionOracle provides us with V$ACTIVE_SESSION_HISTORY to get information about the most common wait events, and the SQL statements, database objects, and users responsible for those waits.SQL to find the wait eventsExampleSELECT event, SUM(wait_time + time_waited) total_wait_time FROM v$active_session_history GROUP BY event ORDER BY total_wait_time DESC;To find out the users who experienced the most waits we can use below SQL.ExampleSELECT s.sid, s.username, SUM(a.wait_time + a.time_waited) total_wait_time FROM v$active_session_history a, ... Read More
Problem:You’d like to identify the blocking and the blocked sessions in your database.SolutionWhen we see an enqueue wait event in an Oracle database, the chances are that there is some thing locking or holding up some sessions from executing their SQL statements. When a session waits on an “enqueue” wait event, that session is waiting for a lock that is held by a different session. We can issue the following command to view information about the blocked and the blocking sessions in ORacle.ExampleSELECT DECODE(request, 0, 'Holder: ', 'Waiter: ') || sid sess, id1, id2, lmode, request, ... Read More