MySQL :: MySQL 8.4 参考手册

MySQL 8.4 参考手册 · 中文镜像

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MySQL 8.4 参考手册 / 15 条 SQL 语句 / 15.6 复合语句语法 / 15.6.6 光标

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15.6.6 游标15.6.6 Cursors

MySQL 支持存储程序中的光标。语法与嵌入式 SQL 相同。光标具有以下属性：MySQL supports cursors inside stored programs. The syntax is as in embedded SQL. Cursors have these properties:

非敏感性：服务器可以或不复制其结果表Asensitive: The server may or may not make a copy of its result table
仅读：不可更新。Read only: Not updatable
不可滚动：只能单向遍历，不能跳过行Nonscrollable: Can be traversed only in one direction and cannot skip rows

。光标声明必须出现在处理程序声明之前，变量和条件声明之后。Cursor declarations must appear before handler declarations and after variable and condition declarations.

示例：Example:

CREATE PROCEDURE curdemo()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE a CHAR(16);
  DECLARE b, c INT;
  DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;
  DECLARE cur2 CURSOR FOR SELECT i FROM test.t2;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  OPEN cur1;
  OPEN cur2;

  read_loop: LOOP
    FETCH cur1 INTO a, b;
    FETCH cur2 INTO c;
    IF done THEN
      LEAVE read_loop;
    END IF;
    IF b < c THEN
      INSERT INTO test.t3 VALUES (a,b);
    ELSE
      INSERT INTO test.t3 VALUES (a,c);
    END IF;
  END LOOP;

  CLOSE cur1;
  CLOSE cur2;
END;

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