Error Handling Pl Sql Block
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Churchill Run-time errors arise from design faults, coding mistakes, hardware failures, and many other sources. Although you cannot anticipate all possible errors, you can plan to handle certain kinds pl sql block exception handling of errors meaningful to your PL/SQL program. With many programming languages, unless you pl sql error handling best practices disable error checking, a run-time error such as stack overflow or division by zero stops normal processing and returns control pl sql error handling when others to the operating system. With PL/SQL, a mechanism called exception handling lets you "bulletproof" your program so that it can continue operating in the presence of errors. This chapter discusses the following oracle pl sql error handling topics: Overview of PL/SQL Error Handling Advantages of PL/SQL Exceptions Predefined PL/SQL Exceptions Defining Your Own PL/SQL Exceptions How PL/SQL Exceptions Are Raised How PL/SQL Exceptions Propagate Reraising a PL/SQL Exception Handling Raised PL/SQL Exceptions Tips for Handling PL/SQL Errors Overview of PL/SQL Error Handling In PL/SQL, a warning or error condition is called an exception. Exceptions can be internally defined (by the run-time system) or
Pl Sql Error Handling Example
user defined. Examples of internally defined exceptions include division by zero and out of memory. Some common internal exceptions have predefined names, such as ZERO_DIVIDE and STORAGE_ERROR. The other internal exceptions can be given names. You can define exceptions of your own in the declarative part of any PL/SQL block, subprogram, or package. For example, you might define an exception named insufficient_funds to flag overdrawn bank accounts. Unlike internal exceptions, user-defined exceptions must be given names. When an error occurs, an exception is raised. That is, normal execution stops and control transfers to the exception-handling part of your PL/SQL block or subprogram. Internal exceptions are raised implicitly (automatically) by the run-time system. User-defined exceptions must be raised explicitly by RAISE statements, which can also raise predefined exceptions. To handle raised exceptions, you write separate routines called exception handlers. After an exception handler runs, the current block stops executing and the enclosing block resumes with the next statement. If there is no enclosing block, control returns to the host environment. In the example below, you calculate and store a price-to-earnings ratio for a company with ticker symbol XYZ. If the company has zero earnings, the predefined excepti
are called exceptions. Note: The language of warning and error messages depends on the NLS_LANGUAGE parameter. For information about this parameter, see Oracle Database
Error Handling T Sql
Globalization Support Guide. Topics Compile-Time Warnings Overview of Exception Handling Internally Defined Exceptions error handling transact sql Predefined Exceptions User-Defined Exceptions Redeclared Predefined Exceptions Raising Exceptions Explicitly Exception Propagation Unhandled Exceptions Error Code and Error Message pl sql raise exception Retrieval Continuing Execution After Handling Exceptions Retrying Transactions After Handling Exceptions See Also: "Exception Handling in Triggers" "Handling FORALL Exceptions After FORALL Statement Completes" Tip: If you have problems creating or https://docs.oracle.com/cd/B10500_01/appdev.920/a96624/07_errs.htm running PL/SQL code, check the Oracle Database trace files. The USER_DUMP_DEST initialization parameter specifies the current location of the trace files. You can find the value of this parameter by issuing SHOW PARAMETER USER_DUMP_DEST. For more information about trace files, see Oracle Database Performance Tuning Guide. Compile-Time Warnings While compiling stored PL/SQL units, the PL/SQL compiler generates warnings for conditions that are not serious https://docs.oracle.com/cloud/latest/db112/LNPLS/errors.htm enough to cause errors and prevent compilation—for example, using a deprecated PL/SQL feature. To see warnings (and errors) generated during compilation, either query the static data dictionary view *_ERRORS (described in Oracle Database Reference) or, in the SQL*Plus environment, use the command SHOW ERRORS. The message code of a PL/SQL warning has the form PLW-nnnnn. For the message codes of all PL/SQL warnings, see Oracle Database Error Messages. Table 11-1 summarizes the categories of warnings. Table 11-1 Compile-Time Warning Categories Category Description Example SEVERE Condition might cause unexpected action or wrong results. Aliasing problems with parameters PERFORMANCE Condition might cause performance problems. Passing a VARCHAR2 value to a NUMBER column in an INSERT statement INFORMATIONAL Condition does not affect performance or correctness, but you might want to change it to make the code more maintainable. Code that can never run By setting the compilation parameter PLSQL_WARNINGS, you can: Enable and disable all warnings, one or more categories of warnings, or specific warnings Treat specific warnings as errors (so that those conditions must be corrected before you can compile the PL/SQL unit) You can set the value of
| PL/SQL Exception Handling Exception Handling In this section we will discuss about the following, 1) What is Exception Handling. 2) Structure of Exception Handling. 3) Types of Exception Handling. 1) What is Exception Handling? http://plsql-tutorial.com/plsql-exception-handling.htm PL/SQL provides a feature to handle the Exceptions which occur in a PL/SQL Block known as exception Handling. Using Exception Handling we can test the code and avoid it from exiting abruptly. When http://psoug.org/reference/exception_handling.html an exception occurs a messages which explains its cause is recieved. PL/SQL Exception message consists of three parts. 1) Type of Exception 2) An Error Code 3) A message By Handling the exceptions error handling we can ensure a PL/SQL block does not exit abruptly. 2) Structure of Exception Handling. General Syntax for coding the exception section DECLARE Declaration section BEGIN Exception section EXCEPTION WHEN ex_name1 THEN -Error handling statements WHEN ex_name2 THEN -Error handling statements WHEN Others THEN -Error handling statements END; General PL/SQL statments can be used in the Exception Block. When an exception is raised, Oracle searches for an pl sql error appropriate exception handler in the exception section. For example in the above example, if the error raised is 'ex_name1 ', then the error is handled according to the statements under it. Since, it is not possible to determine all the possible runtime errors during testing fo the code, the 'WHEN Others' exception is used to manage the exceptions that are not explicitly handled. Only one exception can be raised in a Block and the control does not return to the Execution Section after the error is handled. If there are nested PL/SQL blocks like this. DELCARE Declaration section BEGIN DECLARE Declaration section BEGIN Execution section EXCEPTION Exception section END; EXCEPTION Exception section END; In the above case, if the exception is raised in the inner block it should be handled in the exception block of the inner PL/SQL block else the control moves to the Exception block of the next upper PL/SQL Block. If none of the blocks handle the exception the program ends abruptly with an error. 3) Types of Exception. There are 3 types of Exceptions. a) Named System Exceptions b) Unnamed System Exceptions c) User-defined Exceptions a) Named System Exceptions System exceptions are
Functions PSOUG Forum Oracle Blogs Search the Reference Library pages: FreeOracle MagazineSubscriptionsand Oracle White Papers Oracle Exception Handling Version 11.1 General NOTE: How Oracle Does Implicit Rollbacks Before executing an INSERT, UPDATE, or DELETE statement, Oracle marks an implicit savepoint (unavailable to you). If the statement fails, Oracle rolls back to the savepoint. Normally, just the failed SQL statement is rolled back, not the whole transaction. However, if the statement raises an unhandled exception, the host environment determines what is rolled back. If you exit a stored subprogram with an unhandled exception, PL/SQL does not assign values to OUT parameters. Also, PL/SQL does not roll back database work done by the subprogram. At the level of the SQL*Plus prompt, every update/insert/delete has one implicit savepoint, and also the invocation of any unnamed block. Below that, the unnamed block itself has 'sub' savepoints - one foreach insert/update/delete statement in it, and one for each subprogram unit. And so on down the line. If an error occurs, and that error is handled at any level by the time we're back at the SQL*Plus prompt, we only rollback to the immediate savepoint at the start of the update/insert/delete that errors. Otherwise we rollback to the top-level 'virtual' savepoint currently in existence, which is my offending unnamed block. That is, a handled error is handled and so can be dealt with without rolling back all the way to the top. It is handled and the transaction proceeds. Commits define the end of a transaction (and start of a new one) - rollbacks only define the end of a transaction if they rollback to the last commit, rather than savepoint (whether explicit or implicit). I came to my 'version' from the following by no means exhaustive tests: CASE 1: I created a table a with one column, a1 number, and at the sqlplus prompt inserted a row with a1 = 1. I then ran that unnamed block I referred in an earlier post that, without an exception handler, does the following: INSERT INTO a VALUES (2); INSERT INTO a VALUES (3); INSERT INTO a VALUES ('a'); As expected I get an unhandled error on the last line. When I do a select for everything in the table a, I get the first row I inserted 'manually', the one with a1 = 1. So there seems to have been an invisible savepoint set just before the unnamed block ran.