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PL/SQL Insert. The Insert statement is part of Data Manipulation Language and allows the user to insert a single record or multiple records into a table. In static SQL we had to specify the value for bind variable after execution of the PL/SQL program. While in Dynamic SQL we have to mention the values beforehand for all the bind variables. The same ones that are used in the SQL statement which we desire to execute dynamically using Execute Immediate. Oracle Database PL/SQL Language Reference for information on using the BULK COLLECT clause to return multiple values to collection variables multitableinsert In a multitable insert, you insert computed rows derived from the rows returned from the evaluation of a subquery into one or more tables.

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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.

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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 −

  • The DEFAULT keyword

  • The assignment operator

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 −

  • Local variables − Variables declared in an inner block and not accessible to outer blocks.

  • Global variables − Variables declared in the outermost block or a package.

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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APPLIES TO: SQL Server 2016 and later Azure SQL Database Azure Synapse Analytics (SQL DW) Parallel Data Warehouse

There are three ways to create a system-versioned temporal table with regards to how the history table is specified:

  • Temporal table with an anonymous history table: you specify the schema of the current table and let the system create a corresponding history table with auto-generated name.
  • Temporal table with a default history table: you specify the history table schema name and table name and let the system create a history table in that schema.
  • Temporal table with a user-defined history table created beforehand: you create a history table that fits best your needs and then reference that table during temporal table creation.

Creating a temporal table with an anonymous history table

Insert

Creating a temporal table with an 'anonymous' history table is a convenient option for quick object creation, especially in prototypes and test environments. It is also the simplest way to create a temporal table since it doesn't require any parameter in SYSTEM_VERSIONING clause. In the example below, a new table is created with system-versioning enabled without defining the name of the history table.

Important remarks

  • A system-versioned temporal table must have a primary key defined and have exactly one PERIOD FOR SYSTEM_TIME defined with two datetime2 columns, declared as GENERATED ALWAYS AS ROW START / END
  • The PERIOD columns are always assumed to be non-nullable, even if nullability is not specified. If thePERIOD columns are explicitly defined as nullable, the CREATE TABLE statement will fail.
  • The history table must always be schema-aligned with the current or temporal table, in terms of number of columns, column names, ordering and data types.
  • An anonymous history table is automatically created in the same schema as current or temporal table.
  • The anonymous history table name has the following format: MSSQL_TemporalHistoryFor_<current_temporal_table_object_id>_[suffix]. Suffix is optional and it will be added only if the first part of the table name is not unique.
  • The history table is created as a rowstore table. PAGE compression is applied if possible, otherwise the history table will be uncompressed. For example, some table configurations, such as SPARSE columns, do not allow compression.
  • A default clustered index is created for the history table with an auto-generated name in format IX_<history_table_name>. The clustered index contains the PERIOD columns (end, start).
  • To create the current table as a memory-optimized table, see System-Versioned Temporal Tables with Memory-Optimized Tables.

Creating a temporal table with a default history table

Creating a temporal table with a default history table is a convenient option when you want to control naming and still rely on the system to create the history table with the default configuration. In the example below, a new table is created with system-versioning enabled with the name of the history table explicitly defined.

Important remarks

The history table is created using the same rules as apply to creating an 'anonymous' history table, with the following rules that apply specifically to the named history table.

  • The schema name is mandatory for the HISTORY_TABLE parameter.
  • If the specified schema does not exist, the CREATE TABLE statement will fail.
  • If the table specified by the HISTORY_TABLE parameter already exists, it will be validated against the newly created temporal table in terms of schema consistency and temporal data consistency. If you specify an invalid history table, the CREATE TABLE statement will fail.

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Creating a temporal table with a user-defined history table

Creating a temporal table with user-defined history table is a convenient option when the user wants to specify a history table with specific storage options and additional indexes. In the example below, a user-defined history table is created with a schema that is aligned with the temporal table that will be created. To this user-defined history table, a clustered columnstore index and additional non clustered rowstore (B-tree) index is created for point lookups. After this user-defined history table is created, the system-versioned temporal table is created specifying the user-defined history table as the default history table.

Important remarks

  • If you plan to run analytic queries on the historical data that employs aggregates or windowing functions, creating a clustered columnstore as a primary index is highly recommended for compression and query performance.
  • If the primary use case is data audit (i.e. searching for historical changes for a single row from the current table), then a good choice is to create rowstore history table with a clustered index
  • The history table cannot have a primary key, foreign keys, unique indexes, table constraints or triggers. It cannot be configured for change data capture, change tracking, transactional or merge replication.

Alter non-temporal table to be a system-versioned temporal table

When you need to enable system-versioning using an existing table, such as when you wish to migrate a custom temporal solution to built-in support.For example, you may have a set of tables where versioning is implemented with triggers. Rsa public key generation. Using temporal system-versioning is less complex and provides additional benefits including:

  • Immutable history
  • New syntax for time-travelling queries
  • Better DML performance
  • Minimal maintenance costs

When converting an existing table, consider using the HIDDEN clause to hide the new PERIOD columns (the datetime2 columns SysStartTime and SysEndTime) to avoid impacting existing applications that do not explicitly specify column names (e.g. SELECT * or INSERT without column list) are not designed to handle new columns.

Adding versioning to non-temporal tables

If you want to start tracking changes for a non-temporal table that contains the data, you need to add the PERIOD definition and optionally provide a name for the empty history table that SQL Server will create for you:

Important

The precision for DATETIME2 must align with the precision for the underlying table - see following remarks.

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Important remarks

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  • Adding non-nullable columns with defaults to an existing table with data is a size of data operation on all editions other than SQL Server Enterprise Edition (on which it is a metadata operation). With a large existing history table with data on SQL Server Standard Edition, adding a non-null column can be an expensive operation.
  • Constraints for period start and period end columns must be carefully chosen:
    • Default for start column specifies from which point in time you consider existing rows to be valid. It cannot be specified as a datetime point in the future.
    • End time must be specified as the maximum value for a given datetime2 precision, for example 9999-12-31 23:59:59 or 9999-12-31 23:59:59.9999999.
  • Adding period will perform a data consistency check on the current table to make sure that the defaults for period columns are valid.
  • When an existing history table is specified when enabling SYSTEM_VERSIONING, a data consistency check will be performed across both the current and the history table. It can be skipped if you specify DATA_CONSISTENCY_CHECK = OFF as an additional parameter.

Migrate existing tables to built-in support

This example shows how to migrate an existing solution based on triggers to build-in temporal support. For this example, we assume that the current custom solution splits the current and historical data in two separate user tables (ProjectTaskCurrent and ProjectTaskHistory). If your existing solution uses single table to store actual and historical rows, then you should split the data into two tables prior to the migration steps shown in this example:

Important remarks

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  • Referencing existing columns in PERIOD definition implicitly changes generated_always_type to AS_ROW_START and AS_ROW_END for those columns.
  • Adding PERIOD will perform a data consistency check on current table to make sure that the existing values for period columns are valid
  • It is highly recommended to set SYSTEM_VERSIONING with DATA_CONSISTENCY_CHECK = ON to enforce data consistency checks on existing data.
  • If hidden columns are preferred, use the command ALTER TABLE [tableName] ALTER COLUMN [columnName] ADD HIDDEN;.

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