IF NOT EXISTS SyntaxError in 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

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