How to cycle with an array in MySQL?

All we need is an easy explanation of the problem, so here it is.

I’d like to create a stored procedure or a normal query with values passed with an array.

Example:

CREATE PROCEDURE proc() 
BEGIN 
    DECLARE cont INTEGER; 
    DECLARE var ARRAY; 
    SET cont = 0;
    SET var = ("hi", "hello", "good", ...)

    WHILE cont < 12 DO 
        SELECT * FROM tablex
        WHERE name = var[cont];
        SET cont = cont + 1; 
    END WHILE; 
END;

Obviously this is will not work, but I’d like to know how to achieve this.

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

Try to do it without stored routine –

SET @arr = 'hi,hello,good'; -- your array

SELECT COUNT(*) FROM tablex
  WHERE FIND_IN_SET (name, @arr); -- calculate count

Method 2

Neither of existing answers worked for me, so I ended up implementing my very own (and very first) MySQL procedure.

PROCEDURE db.loop_through_array()
BEGIN
  DECLARE var varchar(150) DEFAULT 'hi,hello,good';
  DECLARE element varchar(150);

  WHILE var != '' DO
    SET element = SUBSTRING_INDEX(var, ',', 1);      
    SELECT * FROM tablex WHERE name = element;
    
    IF LOCATE(',', var) > 0 THEN
      SET var = SUBSTRING(var, LOCATE(',', var) + 1);
    ELSE
      SET var = '';
    END IF;
  END WHILE;
END

Method 3

Try something like this:

CREATE PROCEDURE proc()
BEGIN 
    DECLARE cont INTEGER; 
    SET cont = 0;
    CREATE TEMPORARY TABLE array_table (idx INT, value VARCHAR(20));
    INSERT INTO array_table (idx, value) VALUES (1,"hi"),(2,"hello"),(3,"good"),...;
    WHILE cont < 12 DO 
        SELECT * FROM tablex
        WHERE name IN (SELECT value FROM array_table WHERE idx = cont);
        SET cont = cont + 1; 
    END WHILE; 
END;

Method 4

an example of WHILE loop inside stored procedure:

DELIMITER $$
DROP PROCEDURE IF EXISTS WhileLoopProc$$
CREATE PROCEDURE WhileLoopProc()
      BEGIN
              DECLARE x  INT;
              DECLARE str  VARCHAR(255);
              SET x = 1;
              SET str =  '';
              WHILE x  <= 5 DO
                          SET  str = CONCAT(str,x,',');
                          SET  x = x + 1; 
              END WHILE;
              SELECT str;
      END$$
DELIMITER ;

you can check this article for examples of arrays.

Method 5

Relational databases don’t do arrays, they do scalars, rows and tables. SQL is largely a declarative, rather than procedural, language.

To count entries in a table, use the COUNT aggregate function:

SELECT COUNT(*)
  FROM tablex
  WHERE name IN ("hi", "hello", "good", ...)

If you need to handle a variable number of values to match against in a single statement, you can create a temporary table to hold the values instead of using IN:

SELECT COUNT(*)
  FROM tablex
  JOIN names ON tablex.name=names.name

Method 6

If you can create a table to store the array values you can do it without writing a loop. Use in() operator.

CREATE TABLE test_strings (element CHAR(6));
INSERT INTO  test_strings (element) VALUES ('hi'),('hello'),('good');

SELECT * FROM tablex t
    WHERE name IN(SELECT element FROM test_strings)
    ORDER BY t.name;

Method 7

I guess that you just want to:

SELECT * FROM tablex
WHERE name IN ('hi', 'hello', 'good', ...)

Do you have a problem with how to pass an array to a procedure?

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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