array of mysql stored procedures

MySQL's stored procedure is a set of SQL statements stored in the database that can be repeatedly called and executed. The syntax for defining stored procedures in MySQL is basically the same as functions, but stored procedures can contain more SQL statements and control statements, so more complex operations can be completed. In MySQL stored procedures, arrays are widely used for data storage, reading, modification and deletion. This article will delve into arrays in MySQL stored procedures, including the definition of arrays, operations on arrays, and use cases for arrays.

1. Definition of Array

An array is an ordered data structure consisting of serially connected data elements of the same data type. In MySQL stored procedures, arrays can be implemented by variables or tables. Arrays implemented by variables can define one-dimensional or multi-dimensional arrays; arrays implemented by tables can define table arrays. The definition methods of these three arrays are introduced below.

1. One-dimensional array

In MySQL stored procedures, one-dimensional arrays can be implemented by variables. The method of defining a one-dimensional array is similar to defining a variable. You only need to add brackets [] after the variable name and specify the length of the array in the brackets. For example, define a one-dimensional integer array:

DECLARE arr1 INT[5];

where arr1 is the array name, INT is the data type, and 5 is the array length. You can use a loop statement to traverse the array, for example:

DECLARE i INT;
SET i = 1;
WHILE i

SET arr1[i] = i;
SET i = i+1;

END WHILE;

The above code assigns 1~5 to each element of the array.

2. Multi-dimensional array

In MySQL stored procedures, multi-dimensional arrays can be implemented by nested definitions of one-dimensional arrays. For example, define a two-dimensional integer array:

DECLARE arr2 INT3;

where arr2 is the array name, INT is the data type, and 3 and 4 are the lengths of the two dimensions. You can use a double loop statement to traverse the array, for example:

DECLARE i INT;
DECLARE j INT;
SET i = 1;
WHILE i

SET j = 1;
WHILE j <= 4 DO
    SET arr2[i][j] = i*j;
    SET j = j+1;
END WHILE;
SET i = i+1;

END WHILE;

The above code assigns each element of the array to the product of the number of rows and columns in which it is located.

3. Table array

In MySQL stored procedures, a table array is an array composed of multiple tables, each table has the same structure. For example, define a table array containing 3 tables:

DECLARE tab TABLE(

id INT,
name VARCHAR(20),
age INT

);
DECLARE arr3 tab[3];

where, tab is the structure of the table, id, name and age are the column names of the table; arr3 is the name of the table array, and 3 is the length of the array. You can use a loop statement to iterate through each table in the array, for example:

DECLARE i INT;
SET i = 1;
WHILE i

SET @sql = CONCAT('INSERT INTO arr3[', i, '] VALUES(1, "Tom", 20)');
PREPARE stmt FROM @sql;
EXECUTE stmt;
SET i = i+1;

END WHILE;
DEALLOCATE PREPARE stmt;

The above code inserts a piece of data into each table in the table array named arr3.

2. Array operations

Array operations in MySQL stored procedures mainly include array access, modification, and deletion. The methods of these operations are introduced below.

1. Array access

Accessing array elements can be achieved through subscripts, which start from 0. For example, to access the 3rd element of the one-dimensional array arr1:

SELECT arr1[2];

To access the 2nd row and 3rd column element of the two-dimensional array arr2:

SELECT arr22;

Access all data in the second table of table array arr3:

SELECT * FROM arr3[2];

2. Modification of the array

Modifying array elements can be achieved through assignment operations. For example, modify the 4th element of the one-dimensional array arr1:

SET arr1[3] = 10;

Modify the 2nd row and 3rd column element of the two-dimensional array arr2:

SET arr22 = 5;

Modify the age column of the record with id 1 in the third table of table array arr3:

UPDATE arr3[3] SET age = 25 WHERE id = 1;

3. Deletion of array

Deleting array elements can be achieved by assigning the element to NULL or using the DELETE statement. For example, to delete the 2nd element of the one-dimensional array arr1:

SET arr1[1] = NULL;

To delete the 2nd row and 3rd column element of the two-dimensional array arr2:

SET arr22 = NULL;

Delete the record with id 1 in the second table in table array arr3:

DELETE FROM arr3[2] WHERE id = 1;

3. Use cases of arrays

Arrays are widely used in MySQL stored procedures. Two array use cases are introduced below, namely array sorting and array conversion to string.

1. Array sorting

Sorting of one-dimensional arrays can be achieved through loop statements and conditional statements. For example, bubble sort the one-dimensional array arr1:

DECLARE i INT;
DECLARE j INT;
DECLARE temp INT;
SET i = 1;
WHILE i < ;= 4 DO

SET j = i+1;
WHILE j <= 5 DO
    IF arr1[i] > arr1[j] THEN
        SET temp = arr1[i];
        SET arr1[i] = arr1[j];
        SET arr1[j] = temp;
    END IF;
    SET j = j+1;
END WHILE;
SET i = i+1;

END WHILE;

The sorted array output result is:

SELECT * FROM arr1;

2. Array conversion For string

Converting an array to a string can be achieved through loop statements and string functions. For example, convert the one-dimensional array arr1 to a comma-delimited string:

DECLARE i INT;
DECLARE str VARCHAR(100);
SET i = 1;
SET str = '';
WHILE i

IF i = 1 THEN
    SET str = CONCAT(str, arr1[i]);
ELSE
    SET str = CONCAT(str, ',', arr1[i]);
END IF;
SET i = i+1;

END WHILE;
SELECT str;

The converted string output result is:

1,2,3,4,5

4. Summary

This article introduces arrays in MySQL stored procedures, including the definition of arrays, operations on arrays, and use cases of arrays. As an ordered and efficient data storage method, arrays have important application value in the storage process. By reading this article, I believe that readers have mastered the application method of arrays in MySQL stored procedures, and can flexibly apply arrays in actual development to complete more complex operations.

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