MySQL Tutorial

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MySQL Flow Control Statement

MySQL provides several flow control constructs that allow you to control the flow of execution in stored programs. These include the IF statement, CASE statement, LOOP, LEAVE, ITERATE, REPEAT, and WHILE.

Here's a brief overview of each construct:

IF Statement:
The IF statement allows you to execute a set of SQL statements based on a condition. The syntax is as follows:
```
IF expression THEN
   statements;
ELSEIF expression THEN
   statements;
ELSE
   statements;
END IF;
```

CASE Statement:

The CASE statement allows you to perform different actions based on the result of an expression. The syntax is as follows:

CASE case_value
   WHEN when_value THEN statement_list
   [WHEN when_value THEN statement_list] ...
   [ELSE statement_list]
END CASE;

LOOP Statement:
The LOOP statement allows you to execute a set of SQL statements repeatedly. The syntax is as follows:
```
[begin_label:] LOOP
   statement_list
END LOOP [end_label]
```
LEAVE Statement:
The LEAVE statement allows you to exit a loop early. The syntax is as follows:
```
LEAVE label;
```
ITERATE Statement:
The ITERATE statement allows you to start the next iteration of a loop. The syntax is as follows:
```
ITERATE label;
```
REPEAT Statement:
The REPEAT statement allows you to execute a set of SQL statements repeatedly until a condition is true. The syntax is as follows:
```
[begin_label:] REPEAT
   statement_list
UNTIL expression
END REPEAT [end_label]
```
WHILE Statement:
The WHILE statement allows you to execute a set of SQL statements repeatedly as long as a condition is true. The syntax is as follows:
```
[begin_label:] WHILE expression DO
   statement_list
END WHILE [end_label]
```

Here's an example of a stored procedure using some of these constructs:

DELIMITER $$

CREATE PROCEDURE CountToTen()
BEGIN
   DECLARE x INT;
   SET x = 0;
   
   my_loop: LOOP
      IF x >= 10 THEN 
         LEAVE my_loop;
      END IF;
      
      SET x = x + 1;
      SELECT x;
   END LOOP my_loop;
END$$

DELIMITER ;

This stored procedure uses a LOOP to count from 1 to 10. The IF statement is used to exit the loop (LEAVE my_loop;) when x is greater than or equal to 10.

Using IF statements in MySQL:

Use the IF statement in MySQL for conditional execution of statements based on a specified condition.

IF condition THEN
    -- Statements to execute if condition is true
ELSE
    -- Statements to execute if condition is false
END IF;

MySQL CASE statement examples:

The CASE statement in MySQL allows you to perform conditional logic similar to a switch-case statement in other programming languages.

CASE
    WHEN condition1 THEN
        -- Statements for condition1
    WHEN condition2 THEN
        -- Statements for condition2
    ELSE
        -- Statements for other conditions
END CASE;

Control flow in MySQL stored procedures:

Control flow in MySQL stored procedures involves using IF, CASE, and looping constructs to manage the flow of execution based on conditions.

-- Example: Control flow in a stored procedure
IF condition THEN
    -- Statements for true condition
ELSE
    -- Statements for false condition
END IF;

CASE
    WHEN condition1 THEN
        -- Statements for condition1
    WHEN condition2 THEN
        -- Statements for condition2
    ELSE
        -- Statements for other conditions
END CASE;

-- Looping constructs (WHILE, REPEAT, LOOP) can also be used.

Looping constructs in MySQL:

MySQL supports various looping constructs such as WHILE, REPEAT, and LOOP for iterative processing.

-- Example: WHILE loop
WHILE condition DO
    -- Statements to execute while condition is true
END WHILE;

-- Example: REPEAT loop
REPEAT
    -- Statements to execute at least once
UNTIL condition END REPEAT;

-- Example: LOOP
my_loop: LOOP
    -- Statements to execute
    IF condition THEN
        LEAVE my_loop; -- Exit the loop
    END IF;
END LOOP;

Conditional statements in MySQL queries:

Incorporate conditional statements within MySQL queries using CASE for dynamic result sets.

SELECT
    column1,
    column2,
    CASE
        WHEN condition1 THEN 'Value1'
        WHEN condition2 THEN 'Value2'
        ELSE 'DefaultValue'
    END AS new_column
FROM my_table;

Error handling with flow control in MySQL:
- Implement error handling with flow control in MySQL stored procedures using DECLARE CONTINUE HANDLER for specific conditions.
```
DECLARE CONTINUE HANDLER FOR SQLEXCEPTION
    -- Error handling statements here
```
MySQL GOTO statement and alternatives:
- MySQL does not have a direct GOTO statement. Use alternatives such as LEAVE for exiting loops or labeled BEGIN...END blocks for structured control flow.
```
my_label: BEGIN
    -- Statements
    IF condition THEN
        LEAVE my_label; -- Equivalent to GOTO
    END IF;
    -- More statements
END my_label;
```

Advanced flow control in MySQL procedures:

Advanced flow control in MySQL procedures involves combining IF, CASE, and looping constructs to handle complex logic.

IF condition1 THEN
    -- Statements for condition1
ELSEIF condition2 THEN
    -- Statements for condition2
ELSE
    -- Statements for other conditions
END IF;

-- Advanced control flow logic