mysql判断字段存在进行删除

在MySQL中，如果你想删除一个字段，但在操作前需要检查该字段是否真的存在于表中，你可以使用`IF EXISTS`关键字结合`SHOW COLUMNS`或`INFORMATION_SCHEMA.COLUMNS`系统视图来实现这一目的。以下是一个示例：

DELIMITER $$

CREATE PROCEDURE delete_fieldIfExists (IN tableName VARCHAR(255), IN fieldName VARCHAR(255))
BEGIN
   DECLARE columnExists BOOLEAN DEFAULT FALSE;
   SET @sql = CONCAT('SELECT * FROM information_schema.columns WHERE table_name = ''', tableName, ''' AND column_name = ''', fieldName, '''');
   
   PREPARE stmt FROM @sql;
   EXECUTE stmt INTO columnExists;
   DEALLOCATE PREPARE stmt;

   IF columnExists THEN
      SET @dropCommand = CONCAT('ALTER TABLE ', tableName, ' DROP COLUMN ', fieldName);
      PREPARE dropStmt FROM @dropCommand;
      EXECUTE dropStmt;
      DEALLOCATE PREPARE dropStmt;
      SELECT 'Field ' || fieldName || ' has been successfully deleted.';
   ELSE
      SELECT 'Field ' || fieldName || ' does not exist in the table.';
   END IF;
END$$

DELIMITER ;

然后你可以通过调用这个存储过程来执行删除动作，如果字段不存在则不会执行删除：

CALL delete_fieldIfExists('your_table_name', 'your_field_name');