IF NOT EXISTS SyntaxError in MySQL - mysql

Question

I'm trying to write a kind of update SQL to add new columns if they don't already exist.
I've already tried a few things, but nothing works.
If I try an IF NOT EXISTS I always get a syntax error that I can't understand.
IF NOT EXISTS(
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'nutzer'AND table_schema = 'restdb' AND column_name = 'api_nutzer')
THEN
ALTER TABLE `nutzer` ADD `api_nutzer` TINYINT;
END IF;
[SQL] IF NOT EXISTS( SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'nutzer'
AND table_schema = 'restdb'
AND column_name = 'api_nutzer') THEN
ALTER TABLE `nutzer` ADD `api_nutzer` TINYINT;
[Err] 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF NOT EXISTS( SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
' at line 1
If I execute the SELECT directly, I get a result
Does anyone have an idea or know where my mistake is?
I use MySQL Server Version 8.0.22

Answer 1

I have understood that the Exists clause can be used in the WHERE section
SELECT column1 FROM t1 WHERE EXISTS (SELECT * FROM t2);
try to reconstruct your query for captured if the row exists
for example
<i>if( /*begin extra condition*/ Select 1 where exists
(SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'nutzer'
AND table_schema = 'restdb'
AND column_name = 'api_nutzer') = 1 /*end extra condition*/) then
ALTER TABLE `nutzer` ADD `api_nutzer` TINYINT;</i>

Answer 2

Thanks for your help i get an solutuion for my Problem.
DROP PROCEDURE IF EXISTS addCol;
CREATE PROCEDURE addCol(
IN tabelle VarChar(255),
IN spalte VarChar(255),
IN type VarChar(255)
)
BEGIN
IF NOT EXISTS (
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = tabelle
AND TABLE_SCHEMA = 'restdb'
AND COLUMN_NAME = spalte
)
THEN
SET #ddl = CONCAT(' alter table ', tabelle ,' ADD ', spalte, ' ', type);
PREPARE STMT FROM #ddl;
EXECUTE STMT;
END IF;
END