if inside show mysql to create or insert

Question

good afternoon, I need to understand how an if works inside mysql to be able to use as follows.

I have a foreach that only executes after a database select because it leaves an array for this foreach, in this foreach it will run a condition, if a column exists it will insert information into it, if it does not exist it will create the column and then insert information in it, the problem is, if I send two columns of the same name it will create the first and insert in the second will generate error because the column exists, how to see if the column exists before creating without having to do another query and another loop?

SELECT column_name FROM information_schema.COLUMNS
WHERE column_name = 'telefone' AND TABLE_NAME = 'usr_9f8b498a8e2976d3'

SELECT COUNT(COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'usr_9f8b498a8e2976d3' AND COLUMN_NAME = 'telefone'

in these two selects I can bring if there is or not the column, the bottom is faster, in case, I would like at the end of these selects, in the same query, if der TRUE does not create the column but if der false then create the column

sort of like this /a/3774/8939

something like this, only in mysql that works

IF (SELECT COUNT(COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'usr_9f8b498a8e2976d3' AND COLUMN_NAME = 'telefone') THEN
BEGIN
        select * from usr_9f8b498a8e2976d3
END;
ELSE
BEGIN
    select * from usr_9f8b498a8e2976d3
END;
END IF;

I found this code which is exactly how I want it, but I can’t execute alter table and Insert into inside true and false, but true and false work exactly as wish, is there a way to run alter tabble inside true and Insert into false? in case false has to run both alter table and Insert into and true only Insert into

SELECT IF((SELECT COUNT(COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'usr_9f8b498a8e2976d3' AND COLUMN_NAME = 'sobrenome'),(
'true'
),(
'false'
))

Answer 1

searching and very, very, very many tests, I found an alternative, but still not the one I wish

SET @preparedStatement = (SELECT IF((
SELECT COUNT(COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = '$usr_' AND COLUMN_NAME = '" . acent_remove($value) . "'
) > 0,
' ',
'ALTER TABLE $usr_ ADD " . acent_remove($value) . " VARCHAR(99) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL'
));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;

this option works but I don’t know how to put Apas inside the quote because it needs the alter table between ' ' and I need to run ' ' ' '

"ALTER TABLE $usr_ ADD " . acent_remove($value) . " VARCHAR(99) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '" . $array_form_a_index[$index] . "'"

at the end of this '". $array_form_a_index[$index] . " ' I need him to understand the quote of the comment without affecting the double quote because it is inside php with PDO, complicated

$statement = $conect -> prepare("SET @preparedStatement = (SELECT IF((
SELECT COUNT(COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = '$usr_' AND COLUMN_NAME = '" . acent_remove($value) . "'
) > 0,
' ',
'ALTER TABLE $usr_ ADD " . acent_remove($value) . " VARCHAR(99) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL'));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists; ");

I don’t know exactly if in terms of speed and other technical terms this would be the best way, but heredoc is giving syntax error so I figured out how to "escape string" and now it’s working fine

follows finished code

$statement = $conect -> prepare("SET @preparedStatement = (SELECT IF((
SELECT COUNT(COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = '$usr_' AND COLUMN_NAME = '" . acent_remove($value) . "') > 0,
' ',
'ALTER TABLE $usr_ ADD " . acent_remove($value) . " VARCHAR(99) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT \'" . $array_form_a_index[$index] . "\''
));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;");

If someone knows how to do it correctly or if it is right, I accept suggestions. grateful