What Is a Data Control Language?

Data Control Language (DCL: Data Control Language) is a statement used to set or change database user or role permissions. These statements include GRANT, DENY, REVOKE and other statements. By default, only sysadmin, dbcreator, db_owner, or db_securityadmin roles are available. Members have the right to implement the data control language.

Data control language

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Data Control Language (DCL: Data Control Language) is used to set or change

System stored procedures are stored procedures created by the SQL Server system. Its purpose is to be able to easily query information from system tables or complete management tasks related to updating database tables or other system management tasks. System stored procedures can be executed in any database. System stored procedures are created and stored in

Data Control Language Annotation

A comment is a text string (also called a comment) that is not executed in the program code. In SQL Server, you can use two types of comment characters: one is the ANSI standard comment character "-", which is used for single-line comments; the other is the same program comment symbol as C, that is, "/ * * / ".

Data control language variables

Variables are an essential part of a language. There are two forms of variables in the Transact-SQL language, one is a local variable defined by the user, and the other is a global variable provided by the system.

Data control language local variables

A local variable is an object that can have a specific data type, and its scope is limited to the program. Local variables can be used as counters to count the number of loop executions, or to control the number of loop executions. In addition, the use of local variables can also save data values for control flow statement testing and save data values returned by stored procedures. When a local variable is referenced, it must be preceded by the flag "@", and it must be defined with the DECLARE command before it can be used.

Data control language global variables

Global variables are variables used internally by the SQL Server system, and their scope is not limited to a certain program, but any program can be called at any time. Global variables usually store some SQL Server configuration settings and statistics. Users can use the global variables in the program to test the system's set value or the state value after the execution of the Transact-SQL command.

The following points should be noted when using global variables:

Global variables are not defined by the user's program, they are defined at the server level.

Users can only use predefined global variables.

When referring to a global variable, it must start with the tag "@@".

The name of the local variable cannot be the same as the name of the global variable, otherwise unpredictable results will appear in the application.

Data control language operator

Operators are symbols that can be used to perform arithmetic operations, string concatenation, assignment, and comparisons between fields, constants, and variables. In SQL Server 2000, there are six main types of operators: arithmetic operators, assignment operators, bit operators, comparison operators, logical operators, and string concatenation operators.

Arithmetic operator

Arithmetic operators can perform mathematical operations on two expressions, which can be any data type classified by numeric data type. Arithmetic operators include addition (+), subtraction (-), multiplication (*), division (/), and modulus (%).

Assignment operator

There is only one assignment operator in Transact-SQL, the equal sign (=). The assignment operator enables us to assign data values to specific objects. You can also use the assignment operator to establish a relationship between a column header and an expression that defines a value for the column.

Bit operator

Bit operators allow us to perform bit operations between integer or binary data (except for the image data type). In addition, the left and right operands of a bitwise operator cannot be binary data at the same time.

Comparison operator

The comparison operator is used to compare the size or whether the two expressions are the same. The result of the comparison is a Boolean value, that is, TRUE (indicating that the expression is true), FALSE (indicating that the expression is false), and UNKNOWN. Except for expressions of text, ntext, or image data types, comparison operators can be used for all expressions.

Logical Operators

Logical operators can connect multiple logical expressions. Logical operators include operators such as AND, OR, and NOT. Logical operators, like comparison operators, return a Boolean data type with a TRUE or FALSE value.

String concatenation operator

The string concatenation operator allows string concatenation by the plus sign (+), which is called the string concatenation operator. For example, the statement SELECT 'abc' + 'def' results in abcdef.

Operator precedence from high