Mysql链选择查询

我有一个数据库，其中有一个表，看起来有点像这样：

Root   |   Connector
  A    |      B
  B    |      C
  C    |      D
  D    |      E
  E    |      -

所以我想检索任何给定根的链，直到连接器为空

例如：A链表示A->B->C->D->E，而C链表示C->D->E

我正在使用mysql数据库

---

提前感谢

由于MySQL不允许用户创建递归函数，让我向您展示如何使用存储过程：

假设您正在处理的表名为test

DELIMITER $$

DROP PROCEDURE IF EXISTS build_chain$$
CREATE PROCEDURE build_chain(init CHAR(1))
BEGIN
    IF init != '-' THEN
        SET @r := (SELECT DISTINCT(root) FROM test WHERE root = init);
        SET @search_type := TRUE;
        SET @result := @r;
    END IF;

    SET @r := (SELECT DISTINCT(connector) FROM test WHERE root = @r AND connector != '-');
    SET @result = CONCAT_WS('->', @result, @r);
    SET @search_type = IF(@search_type, FALSE, TRUE);
    IF @r IS NOT NULL THEN CALL build_chain('-'); ELSE SELECT @result AS result_chain; END IF;

END$$

DELIMITER ;

用法：

SET max_sp_recursion_depth = 255;
CALL build_chain('a');

结果链存储在@Result变量中

---

注意：您也可以使用MySQL以外的编程语言来构建链。

由于MySQL不允许用户创建递归函数，所以让我向您展示如何使用存储过程：

假设您正在处理的表名为test

DELIMITER $$

DROP PROCEDURE IF EXISTS build_chain$$
CREATE PROCEDURE build_chain(init CHAR(1))
BEGIN
    IF init != '-' THEN
        SET @r := (SELECT DISTINCT(root) FROM test WHERE root = init);
        SET @search_type := TRUE;
        SET @result := @r;
    END IF;

    SET @r := (SELECT DISTINCT(connector) FROM test WHERE root = @r AND connector != '-');
    SET @result = CONCAT_WS('->', @result, @r);
    SET @search_type = IF(@search_type, FALSE, TRUE);
    IF @r IS NOT NULL THEN CALL build_chain('-'); ELSE SELECT @result AS result_chain; END IF;

END$$

DELIMITER ;

用法：

SET max_sp_recursion_depth = 255;
CALL build_chain('a');

结果链存储在@Result变量中

---

注意：您也可以使用MySQL以外的编程语言构建链。

我只是尝试了MySQL中的循环结构，并获得了成功。仅发布到共享-

CREATE PROCEDURE `root_connect`(IN init char(1),OUT str char(15))
BEGIN
    set @startChar:=(select connector from tableName where root = init);
    set @endloop := "no";
    set @fullchar:= @startChar;
    set @newchar:= "";  
    if (@startChar !="-" OR @startChar =null) then 
        WHILE (@endloop = "no") DO                  
            set @newchar :=(select connector from tableName where root = @startChar);       
            if(@newchar = '-') THEN
                set @endloop := "yes";
            else
                set @fullchar:= concat(@fullchar,"-",@newchar);
            end if;         
            set @startChar := @newchar;     
        END WHILE;
    end if;
        select @fullchar;
END

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我刚刚尝试了Mysql中的循环结构，并获得了成功。仅发布到共享-

CREATE PROCEDURE `root_connect`(IN init char(1),OUT str char(15))
BEGIN
    set @startChar:=(select connector from tableName where root = init);
    set @endloop := "no";
    set @fullchar:= @startChar;
    set @newchar:= "";  
    if (@startChar !="-" OR @startChar =null) then 
        WHILE (@endloop = "no") DO                  
            set @newchar :=(select connector from tableName where root = @startChar);       
            if(@newchar = '-') THEN
                set @endloop := "yes";
            else
                set @fullchar:= concat(@fullchar,"-",@newchar);
            end if;         
            set @startChar := @newchar;     
        END WHILE;
    end if;
        select @fullchar;
END

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你在用什么编程语言？你在用什么编程语言。。。我确实创建了这个存储过程，但我无法执行以下命令：SET max\u sp\u recursion\u depth=255；称构建链为“a”；嗨，胡斯尼。。。我确实创建了这个存储过程，但我无法执行以下命令：SET max\u sp\u recursion\u depth=255；称构建链为“a”；