GENERATED ALWAYS BY DEFAULT ON NULL AS IDENTITY ( identityoptions ) Ignoring the identityoptions, which match those of the CREATE SEQUENCE statement, this syntax allows us to use three variations on the identity functionality. PL/SQL Attacks. Understand SQL injection attacks against PL/SQL. PL/SQL, like stored procedures, can be vulnerable to SQL injection attacks.When PL/SQL code integrates user input into a query and executes it, we encounter exactly the same problem we have when we build a classic dynamic query. Guide to Using SQL: Identity Columns There have been many requests for Oracle Rdb to generate unique numbers for use as PRIMARY KEY values. In Rdb 7.1 we chose to implement two models that capture the functionality of most SQL database systems on the market and reflect the current planning for the draft SQL Database Language Standard.
Prerequisites
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For you to insert rows into a table, the table must be in your own schema or you must have the
INSERT object privilege on the table.
For you to insert rows into the base table of a view, the owner of the schema containing the view must have the
INSERT object privilege on the base table. Also, if the view is in a schema other than your own, then you must have the INSERT object privilege on the view.
If you have the
INSERT ANY TABLE system privilege, then you can also insert rows into any table or the base table of any view.
You must also have the
READ or SELECT object privilege on the table into which you want to insert rows if the table is on a remote database.
Conventional and Direct-Path INSERT
You can use the
INSERT statement to insert data into a table, partition, or view in two ways: conventional INSERT and direct-path INSERT . When you issue a conventional INSERT statement, Oracle Database reuses free space in the table into which you are inserting and maintains referential integrity constraints. With direct-path INSERT , the database appends the inserted data after existing data in the table. Data is written directly into data files, bypassing the buffer cache. Free space in the existing data is not reused. This alternative enhances performance during insert operations and is similar to the functionality of the Oracle direct-path loader utility, SQL*Loader. When you insert into a table that has been created in parallel mode, direct-path INSERT is the default.
The manner in which the database generates redo and undo data depends in part on whether you are using conventional or direct-path
INSERT :
Direct-path
INSERT is subject to a number of restrictions. If any of these restrictions is violated, then Oracle Database executes conventional INSERT serially without returning any message, unless otherwise noted:
You cannot query or modify direct-path inserted data immediately after the insert is complete. If you attempt to do so, an
ORA-12838 error is generated. You must first issue a COMMIT statement before attempting to read or modify the newly-inserted data.
See Also:
Pl Sql Insert And Reference Key Generated Always Free
In this chapter, we will discuss Variables in Pl/SQL. A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in PL/SQL has a specific data type, which determines the size and the layout of the variable's memory; the range of values that can be stored within that memory and the set of operations that can be applied to the variable.
The name of a PL/SQL variable consists of a letter optionally followed by more letters, numerals, dollar signs, underscores, and number signs and should not exceed 30 characters. By default, variable names are not case-sensitive. You cannot use a reserved PL/SQL keyword as a variable name.
PL/SQL programming language allows to define various types of variables, such as date time data types, records, collections, etc. which we will cover in subsequent chapters. For this chapter, let us study only basic variable types.
Variable Declaration in PL/SQL
PL/SQL variables must be declared in the declaration section or in a package as a global variable. When you declare a variable, PL/SQL allocates memory for the variable's value and the storage location is identified by the variable name.
The syntax for declaring a variable is −
Where, variable_name is a valid identifier in PL/SQL, datatype must be a valid PL/SQL data type or any user defined data type which we already have discussed in the last chapter. Some valid variable declarations along with their definition are shown below −
When you provide a size, scale or precision limit with the data type, it is called a constrained declaration. Constrained declarations require less memory than unconstrained declarations. For example −
Initializing Variables in PL/SQL
Whenever you declare a variable, PL/SQL assigns it a default value of NULL. If you want to initialize a variable with a value other than the NULL value, you can do so during the declaration, using either of the following −
Pl Sql Insert And Reference Key Generated Always Working
For example −
You can also specify that a variable should not have a NULL value using the NOT NULL constraint. If you use the NOT NULL constraint, you must explicitly assign an initial value for that variable.
It is a good programming practice to initialize variables properly otherwise, sometimes programs would produce unexpected results. Try the following example which makes use of various types of variables −
When the above code is executed, it produces the following result −
Variable Scope in PL/SQL
PL/SQL allows the nesting of blocks, i.e., each program block may contain another inner block. If a variable is declared within an inner block, it is not accessible to the outer block. However, if a variable is declared and accessible to an outer block, it is also accessible to all nested inner blocks. There are two types of variable scope −
Following example shows the usage of Local and Global variables in its simple form −
When the above code is executed, it produces the following result −
Assigning SQL Query Results to PL/SQL Variables
You can use the SELECT INTO statement of SQL to assign values to PL/SQL variables. For each item in the SELECT list, there must be a corresponding, type-compatible variable in the INTO list. The following example illustrates the concept. Let us create a table named CUSTOMERS −
(For SQL statements, please refer to the SQL tutorial)
Let us now insert some values in the table −
The following program assigns values from the above table to PL/SQL variables using the SELECT INTO clause of SQL −
When the above code is executed, it produces the following result −
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