¿Cómo se asigna un valor a una variable en una declaración de selección en SQL?

How do you assign a value to a variable in a select statement in SQL?

To assign a value to a variable, use the SET statement. This is the preferred method of assigning a value to a variable. A variable can also have a value assigned by being referenced in the select list of a SELECT statement.

Declaring a variable The DECLARE statement initializes a variable by assigning it a name and a data type. The variable name must start with the @ sign. In this example, the data type of the @model_year variable is SMALLINT . By default, when a variable is declared, its value is set to NULL .

Call sqlite3. Cursor. execute(query, parameters) on the previous result with an SQL query named query and with ? characters as wildcards for variable values and parameters as a tuple containing the variables to be used in query to execute a parameterized SQL query in sqlite3 .

Variables in SQL procedures are defined by using the DECLARE statement. Values can be assigned to variables using the SET statement or the SELECT INTO statement or as a default value when the variable is declared. Literals, expressions, the result of a query, and special register values can be assigned to variables.

Passing parameters to SQL queries

1. Passing parameters to a SQL statement happens in functions such as Cursor.execute() by using %s placeholders in the SQL statement, and passing a sequence of values as the second argument of the function.
2. Using characters % , ( , ) in the argument names is not supported.

On the other hand, only one SELECT statement can be used to assign values from the SetVsSelectDemo table to the @EmpName and @EmpGrade SQL variables, using simpler query as shown clearly below:

What to choose when assigning values to SQL Server variables: SET vs SELECT T-SQL statements. SQL Server provides us with two methods in T-SQL to assign a value to a previously created local SQL variable. The first method is the SET statement, the ANSI standard statement that is commonly used for variable value assignment.

If no value is assigned to name, the procedure returns a default value: a numeric function returns 0, a string function returns a zero-length string (“”), and a Variant function returns Empty. A function that returns an object reference returns Nothing if no object reference is assigned to name (using Set) within the Function.

Having no initial value for the @EmpName variable, and no value returned from the subquery, a NULL value will be assigned to that variable in both cases as shown clearly in the result message below: