如果存在,则在mysql中更新

基于对您的问题发表的评论,这里有一个代码片段可以满足您的需求。它首先检查列是否存在于 INFORMATION_SCHEMA ,然后动态构建准备好的SQL查询,然后执行。如果列不存在,将执行一个虚拟查询,而不是 UPDATE . 我测试了它 this db fiddlde .

SET @dbname = DATABASE();
SET @tablename = "my_table";
SET @columnname = "my_column";

-- check if the column exists
SELECT COUNT(*) INTO @cnt 
FROM INFORMATION_SCHEMA.COLUMNS
WHERE
    (table_name = @tablename)
    AND (table_schema = @dbname)
    AND (column_name = @columnname)
    ;

-- build a dynamic SQL statement
SET @preparedStatement = (SELECT IF(
  @cnt > 0,
  CONCAT("UPDATE ", @tablename, " SET ", @columnname, " = '' WHERE my_code = 21;"),
  "SELECT 1"
));

-- run the statement
PREPARE updateIfExists FROM @preparedStatement;
EXECUTE updateIfExists;
DEALLOCATE PREPARE updateIfExists;