1

In MySQL 8.0+ using ROW_NUMBER() window function in each table to get a row number and join the tables on that for row to column transformation from different tables (pivot-table)

The function working correctly if the 2 tables have the same number of rows, like your sample data.

WITH 
  cte1 AS (SELECT *, ROW_NUMBER() OVER (ORDER BY sID) rn FROM t_contents_q400),
  cte2 AS (SELECT *, ROW_NUMBER() OVER (ORDER BY sID) rn FROM t_contents_q410)
SELECT 
c1.contents Q400, 
c2.contents Q410
FROM cte1 c1 
INNER JOIN cte2 c2 ON c2.rn = c1.rn;

+-----------------------+-----------------------+
| Q400                  | Q410                  |
+-----------------------+-----------------------+
| Set n.1               | Set n.1               |
| - Par 1.1             | - Par 1.1             |
| <b>bold text</b>      | <b>bold text</b>      |
| - Par 1.2             | - Par 1.2             |
| normal text           | normal text           |
| Set n.2               | Set n.2               |
| - Par 2.1             | - Par 2.1             |
| <i>italic text</i>    | <i>italic text</i>    |
| - Par 2.2             | - Par 2.2             |
| <u>underline text</u> | <u>underline text</u> |
| - Par 2.3             | - Par 2.3             |
+-----------------------+-----------------------+
11 rows in set (0.03 sec)

But if the 2 tables have the different number of rows some rows are not merged.

On my case I have in the first table t_contents_q400 14 rows total and in the second table t_contents_q410 I have 11 rows total.

On the return these rows of the first table t_contents_q400 are not extract.

Set n.3         Q400
- Par 3.1       Q400
<i>text</i>     Q400

My structures and data tables below

-- ----------------------------
-- Table structure for t_contents_q400
-- ----------------------------
DROP TABLE IF EXISTS `t_contents_q400`;
CREATE TABLE `t_contents_q400`  (
  `contents` varchar(255) DEFAULT NULL,
  `sUnity` varchar(50) DEFAULT NULL,
  `sID` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`sID`) USING BTREE,
  UNIQUE INDEX `contents`(`contents`, `sUnity`) USING BTREE
) ENGINE = InnoDB;

-- ----------------------------
-- Records of t_contents_q400
-- ----------------------------
INSERT INTO `t_contents_q400` VALUES ('- Par 1.1', 'Q400', 1);
INSERT INTO `t_contents_q400` VALUES ('- Par 1.2', 'Q400', 2);
INSERT INTO `t_contents_q400` VALUES ('- Par 2.1', 'Q400', 3);
INSERT INTO `t_contents_q400` VALUES ('- Par 2.2', 'Q400', 4);
INSERT INTO `t_contents_q400` VALUES ('- Par 2.3', 'Q400', 5);
INSERT INTO `t_contents_q400` VALUES ('- Par 3.1', 'Q400', 6);
INSERT INTO `t_contents_q400` VALUES ('<b>bold text</b>', 'Q400', 7);
INSERT INTO `t_contents_q400` VALUES ('<i>italic text</i>', 'Q400', 8);
INSERT INTO `t_contents_q400` VALUES ('<i>text</i>', 'Q400', 9);
INSERT INTO `t_contents_q400` VALUES ('<u>underline text</u>', 'Q400', 10);
INSERT INTO `t_contents_q400` VALUES ('normal text', 'Q400', 11);
INSERT INTO `t_contents_q400` VALUES ('Set n.1', 'Q400', 12);
INSERT INTO `t_contents_q400` VALUES ('Set n.2', 'Q400', 13);
INSERT INTO `t_contents_q400` VALUES ('Set n.3', 'Q400', 14);

-- ----------------------------
-- Table structure for t_contents_q410
-- ----------------------------
DROP TABLE IF EXISTS `t_contents_q410`;
CREATE TABLE `t_contents_q410`  (
  `contents` varchar(255) DEFAULT NULL,
  `sUnity` varchar(50) DEFAULT NULL,
  `sID` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`sID`) USING BTREE,
  UNIQUE INDEX `contents`(`contents`, `sUnity`) USING BTREE
) ENGINE = InnoDB;

-- ----------------------------
-- Records of t_contents_q410
-- ----------------------------
INSERT INTO `t_contents_q410` VALUES ('- Par 1.1', 'Q410', 1);
INSERT INTO `t_contents_q410` VALUES ('- Par 1.2', 'Q410', 2);
INSERT INTO `t_contents_q410` VALUES ('- Par 2.1', 'Q410', 3);
INSERT INTO `t_contents_q410` VALUES ('- Par 2.2', 'Q410', 4);
INSERT INTO `t_contents_q410` VALUES ('- Par 2.3', 'Q410', 5);
INSERT INTO `t_contents_q410` VALUES ('<b>bold text</b>', 'Q410', 6);
INSERT INTO `t_contents_q410` VALUES ('<i>italic text</i>', 'Q410', 7);
INSERT INTO `t_contents_q410` VALUES ('<u>underline text</u>', 'Q410', 8);
INSERT INTO `t_contents_q410` VALUES ('normal text', 'Q410', 9);
INSERT INTO `t_contents_q410` VALUES ('Set n.1', 'Q410', 10);
INSERT INTO `t_contents_q410` VALUES ('Set n.2', 'Q410', 11);
Edward Sheriff Curtis
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1 Answers1

1

You essentially want a full join, which MySQL does not support. One method to handle this is union all and aggregation:

SELECT MAX(CASE WHEN which = 'Q400' THEN contents END) as Q400,
       MAX(CASE WHEN which = 'Q401' THEN contents END) as Q401       
c2.contents Q410
FROM ((SELECT 'Q400' as which, c.*,
              ROW_NUMBER() OVER (ORDER BY sID) as seqnum
       FROM t_contents_q400 c
      ) UNION ALL
      (SELECT 'Q401' as which, c.*,
              ROW_NUMBER() OVER (ORDER BY sID) as seqnum
       FROM t_contents_q401 c
      )
     ) q
GROUP BY seqnum;
Gordon Linoff
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