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MS SQL Server – Local Variables

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In Microsoft SQL Server, local variables are temporary storage locations within a stored procedure, batch of SQL code, or user-defined function. They allow you to store and manipulate data temporarily while the code is executing. Here are some key details about local variables in SQL Server:

  1. Declaration:
    • You declare local variables using the DECLARE keyword, followed by the variable name, data type, and an optional assignment of an initial value.
    • Local variables must start with the “@” symbol.DECLARE @VariableName DataType [= InitialValue]; Example:DECLARE @ItemCount INT = 0;
  2. Scope:
    • Local variables are scoped to the block of SQL code in which they are declared. They are only accessible within that block.
  3. Data Types:
    • Local variables can have various data types, including INT, VARCHAR, DATETIME, and more, depending on your specific requirements.
  4. Assignment and Modification:
    • You can assign values to local variables using the SET or SELECT statement.
    • Once assigned, you can modify the value of a local variable during the execution of the code.
    Example:DECLARE @TotalSales DECIMAL(10, 2); SET @TotalSales = 1000.50;
  5. Use Cases:
    • Local variables are commonly used for storing intermediate results, calculations, or parameters within a stored procedure or function.
    • They are also useful for simplifying complex SQL code by storing the results of subqueries or expressions.
  6. Lifetime:
    • The lifetime of a local variable is limited to the duration of the code execution.
    • Once the code block completes execution, the local variable goes out of scope and is no longer accessible.
  7. Performance:
    • Local variables can be more efficient than temporary tables or table variables for storing and manipulating small sets of data during a query execution.
  8. Naming Conventions:
    • It’s a common convention to prefix local variables with “@” to distinguish them from column names or other identifiers in the SQL code.

Local variables in SQL Server are valuable for managing and manipulating data within a specific scope, especially within stored procedures and user-defined functions. They provide a means to store temporary values, perform calculations, and simplify complex queries.