那些遇到过的问题

如果包含json文档作为字符串,如何从MySQL(5.6)列获取值

Pop*_*ppy 23 mysql json

如果包含JSON文档作为字符串,如何从MySQL(5.6)列获取值

例如,如果我们有一个表 - 员工,我们有三列id,名称和教育.和列教育包含数据作为JSON文档

{"ug":"bsc","pg":"mca","ssc":"10th"}
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我需要来自educations专栏的ug和pg的值

我们可以使用MySQL(5.6)查询吗？

Alv*_*ndo 16

为了能够做你想做的事,你需要MySQL 5.7.8+.从5.7.8开始,您可以使用JSON_EXTRACT函数从JSON字符串中提取值:

SELECT JSON_EXTRACT('{"id": 14, "name": "Aztalan"}', '$.name');

+---------------------------------------------------------+
| JSON_EXTRACT('{"id": 14, "name": "Aztalan"}', '$.name') |
+---------------------------------------------------------+
| "Aztalan"                                               |
+---------------------------------------------------------+
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取自这里.

在MySQL 5.6中,您无法获得所需的值,因为MySQL对JSON对象的内容一无所知.所以你的选择是:

Rah*_*hul 14

在MySQL 5.6中,默认情况下默认JSON_EXTRACT不可用.
如果您仍然需要访问MySQL 5.6中的json数据,则需要编写自定义函数.

DELIMITER $$

DROP FUNCTION IF EXISTS `json_extract_c`$$

CREATE DEFINER=`root`@`%` FUNCTION `json_extract_c`(
  details TEXT,
  required_field VARCHAR (255)
) RETURNS TEXT CHARSET latin1
BEGIN
  RETURN TRIM(
    BOTH '"' FROM SUBSTRING_INDEX(
      SUBSTRING_INDEX(
        SUBSTRING_INDEX(
          details,
          CONCAT(
            '"',
            SUBSTRING_INDEX(required_field,'$.', - 1),
            '"'
          ),
          - 1
        ),
        '",',
        1
      ),
      ':',
      - 1
    )
  ) ;
END$$

DELIMITER ;
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这会有所帮助.我已经创建并测试了.

  • 返回值在末尾包含"}"加上给定:{"distance":55.62,"totalDistance":11946.83} JSON_EXTRACT_C(属性,"$ .distance")给出11946.83} (3认同)
  • 这不是特别可靠或正确。`select json_extract_c（'{“ a”：1，“ b”：2}'，“ $ .a”）;`->`2`，`select json_extract_c（'{“ a”：“ 1”}'， “ $ .a”）`->`“ 1`，`select json_extract_c（'{” a“：” a“}'，” $ .a“）`->空字符串。其他提供手滚功能的答案也是基于这个，所以 (2认同)
  • @gaborsch的答案解决了以上所有的例子,应该检查为正确的答案 (2认同)

小智 10

当JSON文本中没有提到元素时,以前的两个答案对我都不起作用.有我改进的功能:

DELIMITER $$

DROP FUNCTION IF EXISTS `json_extract_c`$$

CREATE FUNCTION `json_extract_c`(
details TEXT,
required_field VARCHAR (255)
) RETURNS TEXT CHARSET latin1
BEGIN
  DECLARE search_term TEXT;
  SET details = SUBSTRING_INDEX(details, "{", -1);
  SET details = SUBSTRING_INDEX(details, "}", 1);
  SET search_term = CONCAT('"', SUBSTRING_INDEX(required_field,'$.', - 1), '"');
  IF INSTR(details, search_term) > 0 THEN
    RETURN TRIM(
      BOTH '"' FROM SUBSTRING_INDEX(
        SUBSTRING_INDEX(
          SUBSTRING_INDEX(
            details,
            search_term,
            - 1
          ),
          ',"',
          1
        ),
        ':',
        -1
      )
    );
  ELSE
    RETURN NULL;
  END IF;
END$$

DELIMITER ;
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gab*_*sch 7

这是我用于JSON提取的3个SQL存储函数.它们处理嵌套对象,但只关心键名.键必须是字符串,值可以是字符串,数字或布尔值.数组处理不好,只选择第一个值.NULL如果没有找到值,他们会返回.

第一个,json_extract_1如果有多个具有相同名称的键,则仅选择第一个值.如果你离开这个LIMIT 1子句,如果找到更多的键(安全模式),它会抛出'Subquery返回超过1行'.

第二个,json_extract_m在逗号分隔列表中使用相同的键收集所有值.

第三个json_extract_c 是最慢的,但它也正确地用逗号处理值.如果绝对必要,请使用它,例如文本描述.

对于所有三个,限制是999键.如果为子numbers选择准备表,则可以加快速度.

DELIMITER $$

/*
 * Single-value JSON extract - picks the first value
 */
DROP FUNCTION IF EXISTS `json_extract_1`$$
CREATE FUNCTION `json_extract_1`(json_txt TEXT, search_key VARCHAR (255)) 
    RETURNS TEXT
BEGIN
    RETURN (SELECT TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(SUBSTRING_INDEX(txt,':',-1), '"', 2), '"', -1)) AS val
    FROM (
        SELECT TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(SUBSTRING_INDEX( SUBSTRING_INDEX(json_txt , ',', n), ',',  -1 ), '}', 1), '{', -1)) AS txt
        FROM (SELECT t1.v + t2.v*10 + t3.v*100 AS n
            FROM (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t1,
            (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t2,
            (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t3) numbers
        WHERE CHAR_LENGTH(json_txt ) - CHAR_LENGTH(REPLACE(json_txt , ',', '')) >= n - 1
        AND n>0 ) sp
    WHERE TRIM(SUBSTRING_INDEX(txt,':',1)) = CONCAT('"',search_key,'"')
    LIMIT 1   -- comment out for safe mode
    );
END$$

/*
 * Multi-value JSON extract - collects all values, group_concats them with comma
 */
DROP FUNCTION IF EXISTS `json_extract_m`$$
CREATE FUNCTION `json_extract_m`(json_txt TEXT, search_key VARCHAR (255)) 
    RETURNS TEXT
BEGIN
    RETURN (SELECT GROUP_CONCAT(TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(SUBSTRING_INDEX(txt,':',-1), '"', 2), '"', -1))) AS val
    FROM (
        SELECT TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(SUBSTRING_INDEX( SUBSTRING_INDEX(json_txt , ',', n), ',',  -1 ), '}', 1), '{', -1)) AS txt
        FROM (SELECT t1.v + t2.v*10 + t3.v*100 AS n
            FROM (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t1,
            (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t2,
            (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t3) numbers
        WHERE CHAR_LENGTH(json_txt ) - CHAR_LENGTH(REPLACE(json_txt , ',', '')) >= n - 1
        AND n>0 ) sp
    WHERE TRIM(SUBSTRING_INDEX(txt,':',1)) = CONCAT('"',search_key,'"'));
END$$

/*
 * Comma-safe JSON extract - treats values with commas correctly, but slow like hell
 */
DROP FUNCTION IF EXISTS `json_extract_c`$$
CREATE FUNCTION `json_extract_c`(json_txt TEXT, search_key VARCHAR (255)) 
    RETURNS TEXT
BEGIN
    DROP TEMPORARY TABLE IF EXISTS json_parts;
    DROP TEMPORARY TABLE IF EXISTS json_parts2;
    DROP TEMPORARY TABLE IF EXISTS json_indexes;

    CREATE TEMPORARY TABLE json_parts AS
    SELECT n, IF(INSTR(txt,':')>0 AND (INSTR(txt,',')+INSTR(txt,'{')>0),1,0) AS this_val, IF(INSTR(txt,':')>0 AND (INSTR(txt,',')+INSTR(txt,'{')=0),1,0) AS next_val, IF(INSTR(txt,',')+INSTR(txt,'{')>0,1,0) AS next_key, txt
    FROM (SELECT n, IF(n%2,txt,REPLACE(txt,',','|')) AS txt 
    FROM (SELECT n, TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(json_txt , '"', n), '"',  -1 )) AS txt
        FROM (SELECT t1.v + t2.v*10 + t3.v*100 AS n
        FROM (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t1,
        (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t2,
        (SELECT 0 AS v UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t3) numbers
        WHERE CHAR_LENGTH(json_txt ) - CHAR_LENGTH(REPLACE(json_txt , '"', '')) >= n - 1
        AND n>0) v
        ) v2;
    CREATE TEMPORARY TABLE json_parts2 AS SELECT * FROM json_parts;

    CREATE TEMPORARY TABLE json_indexes AS
    SELECT p1.n, p1.n+1 AS key_idx, MIN(GREATEST(IF(p2.this_val,p2.n,0), IF(p2.next_val,p2.n+1,0))) AS val_idx, p2.this_val AS trim_val
    FROM json_parts p1
    JOIN json_parts2 p2 ON (p1.n < p2.n AND (p2.this_val OR p2.next_val)) 
    WHERE p1.next_key
    GROUP BY p1.n;  

    RETURN (SELECT json_values.v 
        FROM (SELECT p1.txt AS k, REPLACE(IF(i.trim_val, regexp_replace(regexp_replace(p2.txt,'^[: {]+',''),'[, }]+$',''), p2.txt), '|', ',') AS v
            FROM json_indexes i
            JOIN json_parts p1 ON (i.key_idx = p1.n)
            JOIN json_parts2 p2 ON (i.val_idx = p2.n)) json_values
        WHERE json_values.k = search_key);
END$$

DELIMITER ;
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是的,如果有机会,尝试升级到MySQL 5.7,内置函数的工作效率会更高.

  • 最佳解决方案，实际上是迄今为止唯一没有问题的解决方案，谢谢@gaborsch (2认同)

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