Question

我正在尝试编写一个过程，通过添加外键列来更新表，但返回错误。怎么了？

DROP PROCEDURE IF EXISTS tbl_file_add_column_instance_id;
DELIMITER //
    CREATE PROCEDURE tbl_file_add_column_instance_id()
    BEGIN
        IF NOT EXISTS((SELECT column_name FROM information_schema.columns 
        WHERE table_name = 'tbl_file' AND table_schema = 'diginet2' AND column_name = 'instance_id'))
        THEN
            ALTER TABLE tbl_file ADD COLUMN instance_id INT NOT NULL AFTER id;
            ALTER TABLE tbl_file ADD CONSTRAINT id_instance_arq FOREIGN KEY (`instance_id`) REFERENCES `diginet2`.`tbl_instance` (`id`)
                    ON DELETE NO ACTION ON UPDATE NO ACTION;
            -- Set rows that already exist
            SET @query_initial_instance := (SELECT @initial_instance:=id FROM diginet.tbl_instance WHERE instance_status = 1 LIMIT 1);
            IF COUNT(@query_initial_instance) = 1
            THEN
                UPDATE tbl_file SET instance_id = @initial_instance;
            ELSE
                -- fake throw error
                SELECT * FROM diginet_has_none_or_more_than_one_instance;
            END IF;
        END IF; 
    END //
DELIMITER ;

CALL tbl_file_add_column_instance_id();

并且我收到此错误：错误代码1111。组功能的无效使用

Answer 1

如果您想知道有多少行符合WHERE条件，则应在查询中使用COUNT()，而不要使用IF语句。

SET @row_count = (SELECT COUNT(*) FROM diginet.tbl_instance WHERE instance_status = 1)
IF @row_count = 1
THEN 
    UPDATE tbl_file SET instance_id = (SELECT id FROM digitnet.tbl_instance WHERE intance_status = 1);
ELSE
    -- fake throw error
    SELECT * FROM diginet_has_none_or_more_than_one_instance;
END IF

我认为没有合法的方法可以在单个查询中获得计数和唯一值。您可以这样做：

SELECT @row_count := COUNT(*), @initial_instance:=id FROM diginet.tbl_instance WHERE instance_status = 1;

但这违反了ONLY_FULL_GROUP_BY规则。

无效使用组功能。错误代码1111

1 个答案: